LATE PERIOD HELP ME PLEASE

Kaylia
My boyfriend and i have unprotected sex and didnt late more them 10 mins after we stop ik your cherry pop and it bleeds a litte but i started my period the same , date as 4.16.16 and this is a new month and still no period am been stressing about might be pregnant so i took home text sugar one vinegar and they both cam out negative and i wanted to the dollar store and go a test it always came out neg with a super red line 
Why has my period started help ?!?!?!