I have small red spots on my skin. Legs/stomach/neck/foot. But aren't all there at once, once one set of them disappear another comes up. What is it?

See below. These symptoms can only be adequately diagnosed only after a thorough evaluation by your doctor. This may include labs and other satudies. Once all of the information is in, your doctor can let you know what's going on, and what to do to help you.
Hives. Sounds like hives. If they itch, look like a mosquito-bite, and come & go, then it is likely hives. Try an otc antihistamine.