Heavy Period

So I had sex with a guy about 3 months ago, a while after I tested positive for a UTI, got antibiotics for a UTI and took them. My very next period was not normal from my previous periods and way heavier than normal. I am also on day 7, usually it only last 5 days. Anybody have any idea what could be going on?? Could this be STD related? Or just the UTI? Please help!