Red spot on penis, every month. No pain or itch. Shrinks after a day.

Can anybody help me out please.

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I get this recurring red bump every month or so. no pain or itch. it looks and feels like a pimple but doesn't hurt at all. normally shrinks after a day of noticing. goes quicker if apply some tea tree oi or anti fungal cream. a tiny flake is left which takes a few days to disappear. Always the same size. perfect little circle. no joining up of multiple ones. just singular. I thought it was nodular scabies but it doesn't itch. I am sexual active but with same partner for 2 years, any clues? it doesn't last long enough to get a doctor to see it. Thanks