Hello I Had Unprotected Sex Last Month One Week Before

Hello I had unprotected sex last month one week before my period was due and I had a bled the day after the intercourse which I presumed was my period now my period this month was late and when I finally got it, it was heavy red for the first day but only enough to fill a tampon and the next day it was dark brown discharge and nothing more after that. My period normally last 7 days with the first 5 days heavy and last 2 light. What do you think this could be ? Could I be pregnant or have a STI?