Vaginal itching and irritation with no known cause?!

I have been to my OBGYN countless times and have been tested for STD's (that come back negative), yeast infections (that come back negative), and my hormones seem to be normal. My doctor gave me a topical steroid cream to use whenever I needed to. When I used to use it, the itching and irritation would temporarily go away, but nothing seems to help it anymore. I haven't changed soaps or detergents, and I've been with only one sex partner (my husband). Is there some underlying medical condition or something i'm overlooking that could be causing this intense itching and raw irritation (both outside and inside my vagina)? It is affecting my sexual life and personal life drastically...HELP!!!!