unless it was "three paces" bad I'd say that's a pretty common ailment you've got there...
One thing stop douching obgyn even aare aganist douching. Another thing it may be an infection as simple as a yeast. but it sounds like BV (bacterial vaginosis). Make appointment will put you on antibotics such as flagyl or another one but it will go away. no sex or acohol for 7 days though but its worth it
It's quite possible for a doctor to check you for STDs but not to check you for bacterial vaginosis. Call your doc and get swabbed specifically for it.
Douching is not a good idea. Sometimes, that can cause problems like this. There is no need to douche, use perfumed soaps or sprays down there. The vagina is self cleaning, and using things like that just upsets this and causes things like foul odours or BV (which also has a foul odour).
Some women experience a foul odour after each time they have sex. However, a foul odour should never come from that area. We each have our own odours, and although they might not smell too pleasant, they should never been foul or strong, and certainly not a 'fishy' smell. I would suggest seeing your doctor for swabs to check for infection. (not STD)