The tip/head of my penis sometimes burns when erect/aroused. but its hard to pinpoint where it occurs. sometimes it feels like the urethra. sometimes lower near the frenulum. sometimes i have burning pee but im negative for uti/sti/bac prostatitis?

Engorgement: Vascular engorgement from sexual excitation can result in the symptoms you described. If the symptoms abate with sex or masturbation, you need not be concerned. Have a healthy diet, exercise 30 minutes/day, drink plenty of water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. For nutrition: http://www.choosemyplate.gov/. Wish you good health!