What Causes Bleeding After Sex?

The other night when I woke there seemed to be a lot of dry blood on my sheets after having intercourse earlier that night. In the morning, I didn't continue bleeding and I'm still not bleeding. I'm on Lo-Ovral, and I was to start my period now, but I really don't bleed much after being on the pill for over 10 years.This is the first time I've ever had bleeding after or maybe it was during sex. There wasn't any pain during sex. I'm not having any other symptoms. Does this warrant going into to see my gynecologist?