Urgent sick hamster disease/rash?

When I saw my sister's hamster today, he was shaking and making little squeaky coughs constantly. Also when he got closer to me, I noticed a red area behind his ear, and there was no fur there, and it looked oily. I didn't look long, but I think it was a little scabby. I'm not sure if it was behind both ears or not. Only one for sure. I also noticed a smell. I don't know how to explain it, maybe like stale urine or something. He is about 2 years old and a Robo Dwarf hamster. What's wrong with him?