Vaginal discharge with negative STD results?

I have one partner that I ve been sexually active with. A few days after having unprotected sex with him, I start getting vaginal discharge. It s sometimes whitish other times yellowish. No foul odor, no itching, burning or painful urination. Each time this has happened, I ve gone to the doctor to get tested, but the results always come back negative. Is there a such thing as being allergic to someone? I know it sounds crazy but I m starting ti think that s what it is.