Suggest Treatment For Pink Rash On Neck

My 8yr old son has a bright pink rash on his neck. I rubbed it with a wet soapy cloth, and pink came off like it was marker (he didn t have any that morning). He says it really hurts, and after I cleaned it, there was residual light pink left except for a few streaks that were just as bright, and they were also raised. What could this possibly be? A few weeks ago, on his shoulder (same side) he had an oval rash just larger than a quarter, and it was slightly painful and under the skin, a bunch of purple and pink tiny dots, like petechiae. I don t know if they re related but thought I d mention it.