There are various things going on - what area of your penis are you concerned about? Upper- or -lower shaft, all of it, or … ?
What age are you? Has you penis ever received a skin trauma of some kind, such as being cut, accidentally damaged, or suchlike? Do you have skin problems elsewhere on your body?
on the lower shaft of my penis near my pubic area. i am 26 years old. the skin on my penis sometimes get thin and had some cuts after sex or masturbation.
What you are describing would not seem to make sense - I think you need a specialist opinion by seeing a Dermatologist to investigate what is going on