My 6 yr old is waking up with rashes?

She has a cold and cough and the last couple days has been running a low fever intermittently. When her fever hits her especially at night when she's sleeping she wakes up itching all over, I check her over and she has bright red slightly raised blotches all over her body. I'll treat them with an OTC anti itch cream and it usually helps. By morning her skin is clear and smooth. Sounds like an allergic reaction but I have tried to pinpoint it and can't. I think it has something to do with her fevers. Has anyone heard this any ideas?