Suggest Remedy For Fussy Behavior And Rash On Back

My two yr old son has a rash on his back for two days now. He hasn t eaten or drunk anything unusual nor does he have any allergies that we know of. He is getting over a cold .(blocked nose) He has become very irritable in the past three days and has been crying constantly throughout the night (while asleep) and kicking his legs as well as pushing his feet agaisnt any surface he can come across (still asleep). Are these growing pains? And could the rash just be an allergy? I v had chronic eczema all my life, could this just be the start of it for him? Any answers would be appreciated. thank you