Hi I have a real crisis here, here's some background info:

I'm currently 18 and have had only 1 sexual partner who was tested. I'm not on any birth control pill. My periods always delay one week, ex: if I get my period January 1st, it will last about 7 days and the next period will come February 7th-10th.

My last period ended a week ago, and I had sex the day after my period ended. I ended up with a uti the day after I had sex and went to the doctor for antibiotics.

About 2 days after the day I got uti, my vagina started itching around the lips, this lasted for approx 2 days. There was also a lot of discharge, but I always have a lot of discharge after my period.

It has been a week now since my period ended, and I just got a blob of really dark brown/black discharge that looks like old blood. I also have lower back cramps (which I don't get even when I get my period) 5 hours after the first blob of blood, I got another round.. its like.. a blob of brown goo with some old blood in my panties. I got another round the morning after. It comes out like discharge, and I can feel it come out in a blob. When I wiped today, after a bowel movement I noticed a blob of fresh red blood, but not much. Not even dime sized. So far, there has been nothing since then..

Can this be implantation bleeding? Or a uti side effect? And how can I get pregnant the day after my period ends, because my partner did not come, although it was unprotected. He never came. These signs of pregnancy should not come like right after sex right?

I usually get things that look similar to this right after my period ends.. like for 3-4 days after my period... but I was clean from when my period ended until this sudden spotting. What can it be? Please help!!

Did you read this first?
https://www.askmehelpdesk.com/womens-health/implantation-bleeding-31453.html

Yes I've read that, but what can this be, then? Does it have to do with my uti or other things like an infection? I've never had this before so it definitely scares me

Antibiotics can cause a yeast infection. Sounds as though in getting rid of your UTI you got a yeast infection. Call your doctor and ask for diflucan. It is one small pill that will knock out a yeast infection.

It is not implantation bleeding, if you read the thread Val gave you you can clearly see that.

You most likely cannot get pregnant the day after you stop your period as you have not yet ovulated again.

Also, just because he does not orgasm inside you does not mean you will not get pregnant. This is not a method of birth control. There is the issue of pre-ejaculation, prior to orgasm, that all men have and they are usually unaware of it. Pre-ejaculation carries millions of sperm.

So, in ending, this sounds like a simple yeast infection from the antibiotics. Good luck.