I had a blood test & my first ultrasound & I was told by my doctor that I was around 8 weeks & 6 days pregnant. However, 8 weeks & 6 days ago I was on my period & had not had sex since the 21st of the month prior. It makes no sense, could the doctor's be wrong?

Yes, they can be wrong, and they go as much by what you tell about about last period as anything on ultrasound. Tell us all the dates (last sex, beginning of last period, and when you were told 8 weeks 6 days) if you want.
And of course sometimes the woman reporting is wrong about her dates too...

Ok, so I started my last period on the 18-19th of may. It ended on the 25th of may. Before this period I hadn't had sex since the 21st of April. I had unprotected sex using the withdrawal method on the 26th of may (so the day after my period stopped) & had a lot of sex for the entire week (what can I say, it was a great week!) When the doctor told me I was 8 weeks and 6 days, I immediately checked my calendar and there is NO WAY I am 8 weeks 6 days, as I would have still had my period & wouldn't have had intercourse for a month! I was told they usually measure how far you are along by the size of the baby in the ultrasound, is it possible its just growing fast? I'm so confused!

Yes, they can be wrong, and they go as much by what you tell about about last period as anything on ultrasound. Tell us all the dates (last sex, beginning of last period, and when you were told 8 weeks 6 days) if you want.
And of course sometimes the woman reporting is wrong about her dates too...
Ok, so I started my last period on the 18-19th of may. It ended on the 25th of may. Before this period I hadn't had sex since the 21st of April. I had unprotected sex using the withdrawal method on the 26th of may (so the day after my period stopped) & had a lot of sex for the entire week (what can I say, it was a great week!) When the doctor told me I was 8 weeks and 6 days (I was told by the doctor yesterday, the 25th of july), I immediately checked my calendar and there is NO WAY I am 8 weeks 6 days, as I would have still had my period & wouldn't have had intercourse for a month! I was told they usually measure how far you are along by the size of the baby in the ultrasound, is it possible its just growing fast? I'm so confused!

My calculations, as of today, with your LMP being May 19, put you at 9 weeks and 5 days with a conception date of approximately May 30 - June 2.

Remember that conception dates are strictly a guess as there is not a camera in your fallopian tube to know exactly when the sperm meets the egg. Also, it can take as long a 3-5 days for the sperm to reach the egg, then another 3-5 days for the implanted egg to reach the uterus.

With my calculations your due date would be around February 23. You also have to take into account that there is a 2 week window either way.

My calculations, as of today, with your LMP being May 19, put you at 9 weeks and 5 days with a conception date of approximately May 30 - June 2.

Remember that conception dates are strictly a guess as there is not a camera in your fallopian tube to know exactly when the sperm meets the egg. Also, it can take as long a 3-5 days for the sperm to reach the egg, then another 3-5 days for the implanted egg to reach the uterus.

With my calculations your due date would be around February 23. You also have to take into account that there is a 2 week window either way.
I'm still confused! How can I be this far along if I didn't conceive until may 30-June 2nd? I started bleeding around the 19th or 20th, and finished the 25th of may, the next time I had intercourse was the 26th of may, so I can't be that far along! I'm so confused :(

You had intercourse on the 26th of May, you could have gotten pregnant from that encounter. You also said, above, that you were very active that week as well.

You had intercourse on the 26th of May, you could have gotten pregnant from that encounter. You also said, above, that you were very active that week as well. Yes, but counting back 8 weeks & 6 days on my calendar from yesterday, I would still have had my period & hadn't had sex for a month. So it has to be incorrect. Is there something I'm missing or don't know about pregnancy/implantation/conception? This is my first time, I'm only 21 & I'm still so confused! I'm sorry for being a pain! Lol

I think you are just confused. You see, pregnancy is just and educated guessing game. We professionals rely on you to provide us with accurate information, which you did, LMP. However, when we are looking at an ultrasound we are looking at the developing fetus. Each week there is a new system developing in the fetus. So we will see something different if we did ultrasounds every week.

Actually counting back to your period, from yesterday, that was around 9 weeks ago from the very start of your last period.

Most likely you got pregnant with your first encounter after your period. The withdrawal method is not a method of birth control and many people who use it are called parents.

Are you questioning who the father is?

I think you are just confused. You see, pregnancy is just and educated guessing game. We professionals rely on you to provide us with accurate information, which you did, LMP. However, when we are looking at an ultrasound we are looking at the developing fetus. Each week there is a new system developing in the fetus. So we will see something different if we did ultrasounds every week.

Actually counting back to your period, from yesterday, that was around 9 weeks ago from the very start of your last period.

Most likely you got pregnant with your first encounter after your period. The withdrawal method is not a method of birth control and many people who use it are called parents.

Are you questioning who the father is?

Not really - quick back story.
I was with someone, the last time we had intercourse was the 21st of April, we broke up on the 24th of may, at that point I had my period, which started around the 19th, ended the 25th. I caught up with a close friend/ex boyfriend on the 26th & we had sex using the withdrawal method (not the smartest & effective method, I know, hahaha) & then did the same thing over the course of a few weeks. We decided to become a couple again as we never really got over each other, even after dating other people. Soon after I found out I was pregnant. Going back in my calendar 8 weeks & 6 days I would still have had my period & hadn't had sex in a while, so I'm just assuming because my lmp dates are a bit wishy washy (I know when it finished but I'm not 100% on when it started) that the doctor could be wrong. When do doctors start counting when you're pregnant from? Conception? I'm sorry again, I'm new to this & it doesn't make sense to me! :(

Conception... when the sperm meets the egg.

We start counting from the first day of your last period.

The encounter in April did not make you pregnant.

The encounter in April would put you around 16 weeks pregnant.

Conception...when the sperm meets the egg.

We start counting from the first day of your last period.

The encounter in April did not make you pregnant.
OH MY GOD IT ALL MAKES SENSE NOW.
I didn't know that the counting started at the first day of the last period. No wonder nothing made sense!
I feel like such a dork!

It's okay. It's all new to you!

It's okay. It's all new to you!

It definitely makes sense now, hahaha! Thank you so much for your help. Ill definitely talk about it with my doctor as soon as I see her just to verify everything but this that really put my mind at ease :)