How can i tell the difference between heat rash, and a reaction to taking aleve (naproxen). do either require medical attention?

Not enough info: As to skin rashes, seeing IS believing. I recommend that, if you can't get in to see your own doctor, you go to an urgent care center for evaluation. Alternatively, you could do a Virtual Consult with one of our doctors. You would need to do an audiovisual consult and upload a picture of the rash. The urgency depends on the severity of your symptoms.