My son has red flat rash on stomach and back. he is 1, we haven't changed anything. what could be causing this?

Hard to say: Without seeing your child in person, it's impossible to diagnose his rash. Please take him to his Dr. for evaluation.

Don't know: This can't be diagnosed with the information that is available. A history, physical examination & other studies may be needed to determine cause/causes. Once accurately assessed a treatment plan can be developed.