A red spot on the head of the penis can indicate an inflammation caused by mechanical trauma due to masturbation complicated with a local bacteria infection. You can consult your family physician about ceasing the masturbation for a while and using warm water with soap for local hygiene. If these suggestions don’t seem to help, you can ask for more information about local treatment with antibiotic balsams. Or you can always seek the expert advice of an urologist for a visual examination of the affected area.