I have some red spots, like rash, on legs, butt and back. there distant one from other and they are itchy. could they be an allergic reaction (it doesn't look like hives) or is it an insect bite? would an antihistamine help?

Doctor can examine: Antihistamines block the chemical histamine and thus decrease itchiness and decrease allergies. Red spots are hard to describe or diagnose in words, and can be from many causes such as: viral infections, other infections, medication causes, strep throat, hot-tub rashes, heat rashes, reactions to creams or lotions, allergic reactions to various things (including foods), internal disorders, etc...