I'm 26, have relationship the last 1,5years but i see my girlfriend twice a month and we have sex then.

However, the last months i have noticed that when i masturbate or after having sex (sometimes) I see my penis getting shinny red - pinkish on its top side (the side I look when i look down), which goes away after a couple of days.

I have not seen a doc for that since it goes off after some days and it is not causing me any pain or itchyness however i wonder whether it is something serious (thrush maybe?) or if it just gets sensitive and goes red from rubbing'

Any ideas?

Thanks!