Hey, this is my first time here, but I need some help. I'm 15, and I've had lots of sex with my boyfriend, but the only unprotected time was only for a few seconds and just after my period finished - isn't this the most infertile time, before ovulation? Usually I wouldn't worry, and I got my period last month, but it's about a week late this month. As I'm still young, my period is usually irregular, and sometimes doesn't come for a few months, but this month there was some brown spotting as if a period had just ended, and that's never happened before. There was some heavy blood as if a period was starting, but it was gone by the next morning. Maybe it's just paranoia but I'm also feeling some symptoms like bloating, nausea and moodiness. It feels a lot like PMS, but it's going on for a long time. What do you guys think?

Any time you have sex you run the risk of pregnancy. Having unprotected sex skyrockets the risk.

Every woman is different, and you can ovulate at any time during your cycle. But the fact that you had your period the next month, and spotted this month leads me to believe you are not pregnant.
I have irregular periods, and have had them since your age (I'm 25 now). My OBGYN tells me to count ANY show of blood, such a spotting or light flow, as periods regardless of how long they last.

I wouldn't worry over it too much... you seemed to have lucked out this time.

The only safe sex is NO sex.

... the fact that you had your period the next month...

I haven't had a period since the one time, the time happened pretty much the day my last period finished. I was just proving that the only time I could have become pregnant was that day.

Well it only take one time.

Take a HPT to make sure.

Sorry to bother you all again, but after talking to people I have one or two more questions. How long does this "implantation bleeding" last, and what is it like? Heavy or light?

Please read this sticky regarding "implantation bleeding."

https://www.askmehelpdesk.com/womens-health/info-answers-frequently-asked-questions-our-health-expert-53865.html#post250352

Oh, okay. Thank you, that was a little helpful. I'm so sorry, I'll rephrase what I really need to know, and it wasn't exactly answered.

Is it normal, if I am pregnant, to have two or three weeks of said implantation bleeding or spotting (but I wouldn't say spotting, it was really heavy)?