Short period

Normally my periods last 6-7 days, the first, second and third day are always really heavy flow then the rest is just light flow (3rd day starts to get lighter). This time though I was only heavy for the first 2-3 days, I'm on the 4th day now and I'm hardly bleeding...I had unprotected sex on the first two days of my period and a couple weeks before, could that have affected it (mind you he wasn't in for long and pulled out wayyyy before he came outside of me)? I'm pretty sure it isn't implantation bleeding because I still got my usual back cramps and moodiness. Should I be worried?