Bleeding 2 weeks after your period

I had my period 2 weeks ago, started noticing some browish pink blood along with what looks like a little tissue. Its been 4 days, 2 days brownish pink and 2 days with light reddish blood with a little cramping (not as bothersome as my normal period cramps), tiredness, nausea and frequent urinating. Its been only 7 days since the last time i had unprotected sex but i had unprotected sex 3 times in the same week and i am also on birth control pills and haven't missed or been late taking them. I was also on an antibiotic treatment for BV the week before my period but i researched the effects of that exact antibiotic decreasing the effects of birth control but it said that it doesn't. So i finished my 5 day treatment for BV on a sun, got my period that tues on schedule according to my pills, had my period for 5 days (2 days longer then usual) period ended on sat, had unprotected sex on tues then again on friday and sat of that same week then the following thurs i noticed the brownish pink blood and tissue. Took a pregnancy test today (exactly 7 days from the last time i had unprotected sex) and it was negative. What could be the cause of the bleeding if i'm not pregnant?
P.S The blood does not have an odor to it like with a regular period...