so confused

Hi I started my period the 3rd of March and ended the 6th of March and yesterday I had light spotting and today it's heavier like a period my husband and I had unprotected sex the 7,8,9 what could this be? My periods are so irregular I never know when I'm ovulating iv been trying to convince for 4 months now. I've looked up so many things on the internet and can never find an answer.. Could really use some help!