Its normal to spot or bleed after intercourse. Your cervix is more sensitive during pregnancy and any irritation can cause bleeding. Contact your doctor though, like sweetangel said usually with any type of bleeding even if its not serious they like to get you in.
Personally, with a clot, I would be concerned....bleeding, and spotting are considered normal but I'd call your doctor on-call to discuss this since it is the weekend. Also, I'd call your regular ob first thing tomorrow morning so they can make a decision as to whether or not they want to see you. My doctors always see me asap whenever I've had any type of bleeding in the past.