Could it be an Std?

So a few weeks ago I had sex with a guy I met, it was a one time thing. We used a condom but it kept falling off (he was a bit small) and even fell off inside me. I didn’t think much of it tho because I got it out safely. We ending up hiving up on using it🙄 I know I’m dumb.

Well after that my period didn’t come and I started getting worried (I’m in the pill so my period should come on time), I took two pregnancy test, they both came back negative but the first one ended up changing to positive after an hour.

I was also getting funny discharge, it was like brown. And I’d get some toilet paper and put it up me to see what was going on and a bunch of brown stuff came out. Then the brown stuff stopped and My friends told me I had a miscarriage and the same thing happened to her.

Well not it’s been like two weeks and I had sex with another guy on Saturday, now I went to check my self by putting toilet paper up me again and more brown stuff came out and I was bleeding a lot, but there was nothing in my undies.

I’m just a bit confused

Had anyone gone though this?

Also please don’t judge me, last time I put something up on someone was so rude in the comments saying I was dumb and young, I was only 17 then now I’m 18, we all make mistakes and we know what it’s like to get into the moment