I am definitely not pregnant, but my period was 6 days late this month (possibly due to stress and a holiday). For this last few days I have been feeling light cramps but my period wasn't starting. This morning I had sex and my period started a few hours later and was quite heavy but also watery and I have been having usual period cramps. By this evening it's slowed down a lot and is much lighter. I am now really worried if this is even my period or I'm bleeding heavily from the sex and I don't know how to tell the difference.