Bacterial vaginosis is usually the culprit for a smell and dishcharge especially after sex. Since you are pregnant its very important that you see your doctor to get some metronidazole or clyndimicin prescribed to clear it up. It can have adverse affects when you're pregnant and it goes untreated. It is not an STD and isnt usually spread man to woman or vice versa. The bacteria live naturally in the vagina but just like when yeast infections occur it is because of an imbalance in the flora of the vagina.
I had smelly discharge at 6 months....told doctor but he didn't think it was serious...by 7 months it stopped....I was not having sexual intercourse though. I was put off since 20th week...
You may have an infection. Call and make a drs appointment so that they can give you the proper antibiotics for it. Discharge shouldn't have a bad odor. Hope this helps.