Hello,
There can be many differentials for a penis rash depending on the type of symptoms that you have. Please elaborate on the symptoms and description of rash so that a list of differentials can be made.
I hope it helps. Take care and regards.
Tell your parent you need to see the Dr for a personal problem down there that your uncomfortable talking about but need medical assistance. It's really important to be seen by a Dr because depending on what they find it may not resolve itself without medication and there is no other way around that. If you can call the Dr office and speak to the nurse and ask help speaking to your parent if needed. But whatever it takes get yourself to the Dr! goodluck.