My 7 year old son's penis hurts when peeing. Uti is negative.

Balanitis. Your child may have balanitis if he is not circumcised.
See my comment. It is hard to diagnose, is he circumcised? If he is, he may have a smaller than usual opening does the head of the penis look normal, irritated, red give him a tub bath , if it persists, see your pediatrician, or if you can see a urologist.