I get this too I've been tested so many times and nada! find out if you are insulin resistant ask your doc to do some blood tests and if you are start taking diabex an 2000mg per day, that got rid of it for some people. also, visit this forum, it might help
try not to douch anymore its not good for the vaginal flora and can make the odour worse in the long run.
Do you eat much red meat or dairy, because that can be the cause in some cases. cut it out for a day or two and see if your still smelly. i think this is my case(but i cannot smell it i just get comments about a smelly hooha)
one more thing it could be is a candida overgrowth, it can sometimes cause an odour down there, theres a spit test you can do at home i forget where its posted but if you look up, saliva candida-test-glass-water you might find something(without the dashes)I have to say this and the fecal odour i have has ruined my life, i will never be the same. goodluck, try to cut out dairy and meat(my case)