See a doctor to find out what is wrong, as others said. But as far as a lot of fluid, this may be perfectly normal for you and you may just need to always put a thick towel down before intercourse. Guys won't mind.
Even getting tested for sexually transmitted disease won't necessarily catch a bacterial infection like gardnerella, which smells. Tell your ob what is happening and ask for a full range of tests, from yeast to BV.
The discharge immediately after sex is just his stuff coming out since you're not using a condom. Perfectly normal. We both clean off afterward. Sex is messy and I don't really find it a mood killer afterward. We both clean up and go on cuddling.
If you have a bad smelling discharge, however, as you mention, go see your gynecologist. It may be an infection you need to have treated.