Well I went to the doctor because I had a red like rash on the top of my head and she gave me some cream for it and said it wasn't bad but it didn't seem to help until I jacked off like a week ago and now when I sqeeze the bottom of my head it gets purple and doesn't hurt and its only the bottom half turns purple

First, quit squeezing it so hard. It turns purple because of lack of blood flow.

If you have any concerns about your penis, talk to your parents, or doctor.