Ok so this is going to be a lot I'm really confused right now.

So in the beginning of July thats when I had my period for the month and that period lasted 7 days which is usually normal for me or I'll stop sooner then that. But anyways 8 days later I start bleeding again (side note: I am currently taking birth control pills and I have been taking them since December and I've had no problems with this birth control) and it turns out to be another period but this one is going on longer then usually I am on day 9 now but for the last 3 days I've been bleeding out brown blood (sorry tmi) and I keep getting really bad cramps everyday. Like I said ive never this happen before, my birth control has worked great my period always comes at the same time every month except for July. I am also kinda nervous because I did have unprotected sex on July 8 and yes he did cum inside me and the days before I wasn't taking my birth control correctly I would take it late or have to double up the next day. I have taken a pregnancy test before like last week and it came out negative but I do know sometimes pregnancy test could have false negatives .

someone please help me out