It's a mystery!

I have a very strange rash on one of my arms which appeared this morning when I got to school. It starts on my hand and spreads all the way up my forearm, it looks like red dots but they're not raised and it's not itchy but the skins really sensitive. I have no idea what caused it but I'm a bit worried because it hasn't disappeared or lessened yet. Of course, reading up on strange diseases isn't helping at all! I'm relieved it's not hand, foot and mouth disease though. Any ideas? I'm going to the doctor's later to see what he says. The deputy Ms. Wong (not so helpfully) just put Mopiko bite cream on it which only made it burn! I'm my own medical mystery heehee.