I woke up with itchy red bumps on backs of my legs?

Hmm, well im just guessing here, but the bumps may be caused from your body's heat, if you were hot, and blankets/sheets from your bed, rubbing up against each other, i would try a type of soothing cream, lotion, benadryl lotion could help with the itching, or (personally) if i get bumps on my legs/bikini area i use preparation-H, surprisingly, it works really well!