What Causes Ulcer On Foreskin And Glans?

sir i have a ulcer on my foreskin as well as on the glans..they appeared 4-5 days back..initially they were very painful..i applied antbacterial cream..now the pain has subsided..though they are still sensitive when i apply ointment..I am a virgin..so it cannot be STD..I am very tensed..Please suggest..My age is 24 and weight s 62 kg..this is the first occurrence of this sort