I recommend that you go to see a doctor. It could be a vaginal infection.

well... guys semen lasts in your vagina (there's a little culvert up there that collects it) and gets stinky. It stays up there for a few days (Even if it seems like it all comes out, some of it usually hangs in there) Really, if it's only after sex, and you aren't having any other symptoms like funky colored discharge then it's probably just his semen.

you could try a condom and see if that solves it, to rule out everything else.

ok i have a question wat if u get a discharge after u had sex used a condom and the discharge is still there after a week n it gets heavyer n u have abdomenal pain and in your tummy?

Usually discharge is a sign of an infection, I'd suggest you hit up your OBG.

As far as the original poster, the answer is most likely yes, a mixture of your "Goo". The male penis can culture bacteria not native to the insides of your vagina, this can cause something like a light bacterial vaginosis where the normal bacterial level in your vagina elevates, this is where the smell comes in. It goes away when your vagina has settled back to its normal bacterial levels.

A way to combat this is as you said use a condom or both partners bath "well" before intercourse.
-Mr Knight