Get it checked out immediately.
This is probably nothing like what you have at all but my cousin had a rash on his hairline and he had it for a few years and went to the doctor this week about something completely different, the doctor saw it and he is now diagnosed with skin cancer. I've just made an apointment to get my mole that has grown bigger looked at, rather waste the doctors time than risk your own health.
Good luck, I'm sure you'll be fine - Joe