Talk to Urologist on Shrink In Between

My penis will shrink in middle and looks off proportion. I never had any type of sex but masturbate. It happens a lot of time like after I masturbate that will happen or before going to a hot shower or just random times of day when I look at it. When I get an erection my penis is completely normal and nothing wrong. It is only when its in flaccid. Is it harmful? Is my penis damaged because of masturbation? Please help.