The most common causes of vaginal discharge with odor are trichomonas, which is sexually transmitted, and bacterial vaginosis, which may be triggered by sex but isn’t usually an STD in the usual sense. Trich is sort of suggested by yellow or brown discharge that stains clothing, but most cases of trichomonas are pretty easy to diagnose; your doctors should have picked it up. The discharge of BV usually is white or gray and doesn’t stain. But those aren’t the only possibilities. You don’t say whether you are at risk for STD (new partner, multiple partners, past STDs, etc, or a partner at risk), which makes a difference; chlamydia, gonorrhea, and other infections are possible, and so are several other non-STD problems.
It shouldn’t be that difficult to find a knowledgeable health care provider who can figure this out. Good bets are a gynecologist with lots of experience with infectious diseases (check with a major medical center or medical school, if one is in your area); the local health department family planning or STD clinic; or a Planned Parenthood clinic.
Finally, I hope you’re not trying to take care of the problem by douching. It might be tempting; discharge and odor are common reasons women try douches. But douching generally only makes problems like yours worse. If you have been doing it, stop for a few weeks and see if it makes a difference.
Good luck-- HHH, MD