This never happens.

My period is supposed to start on the 16th, I ALWAYS start on time. This morning I had sex with my Fiancé and he came in me (we've decided to try to have another baby) Then 2 hours later I go to the bathroom and I started my period? I don't it was different then normal a little more lighter. And it looked like it was going to be my normal period but then I wiped again and it was a light pink. And it's just stayed that way. What does that mean? I've never had that happen so it was a little weird.