Bleeding and cramps, normal. Sex four days afterwards, no, not normal. You should have been advised not to have sex for 2 weeks afterwards, or until your bleeding had completely stopped - whichever period of time was the longest.
I would suggest you consult the information the clinic gave you as to "when to get in touch with them" regarding symptoms and infection. If you don't have a fever or serious pain, and the bleeding has subsided by now, I think you're fine.
Just abstain from sex until your body has recovered!
Kirsty