I'm confident you don't have yeast, because the treatment you got would have taken care of it. So I think you should get yeast, fungus, or infection off your mind. My experience with red scrotum is that, although cause is unknown, the redness and sensitivity eventually subsides, and the less aggressively you treat it, the better. I advise avoiding any sort of cortisone, however mild, and sticking with mild soaps, bland moisturizers, and perhaps one of the nonsteroidal anti-inflammatory creams like tacrolimus or pimecrolimus. Your dermatologist can tell you about these and perhaps prescribe them. You'll need patience, but you're not infected and in the end you'll be fine.
Take care.
Dr. Rockoff