What’s happening??

Okay so this is probably going to be very confusing I’m not sure how to explain it well. But here I go. So I had PROTECTED sex on March 17th BUT he said the condom slipped of when he pulled out and he wanted to take a pill. I didn’t take a pill because I didn’t think I needed to. The next day I started my period and that lasted about 6 days which is normal for me. The day my period ended, the 23rd I had sex again but this time I was on birth control BUT I had only been on it six days BUT then I heard that it starts working immediately when you start taking it the day your period starts which I did, so I thought I’d be safe. I had unprotected sex Monday night and my fertile window started today. Well all of Tuesday and today I’ve been having light bleeding, not heavy enough for a tampon but there’s blood every time I wipe. I took an early pregnancy test last night and it came back negative (which I suspected it would). I’m just so worried about the bleeding. I don’t know if it’s implantation bleeding, if we just went at it too hard, or if it’s some kind of std???? I don’t know I’m freaking out.