What can cause red raw skin on scrotum underneath penis. full std panel negative. its red with little white bumps?

It is not feasible to provide a meaningful opinion without additional history, physical examination and may be some tests. It would be prudent to see a doctor, preferably a dermatologist. Wish you good health!

Getting an STD panel for your symptoms was a waste of resources. Your MD should have examined and treated you. In all probabilities it is a fungal infection. Clean the area and apply OTC lotrimin or lotrisone cream. If not better in a few days pl see a dermatologist. Hope you do well