Thanks for your query.Based on the facts that you have posted it appears that you have developed red spot on glans
of your penis .
Most likely it is due to infection of the glans (Ballanitis) due to dry vigorous and rough handling of the penis while masturbating.
Please take broad spectrum antibiotics along with anti inflammatory medication like Diclofenac
twice daily .
Get the prescription of medicines from your family Physician.
Ensure to clean your genitals with warm water twice daily.