Small red patches under the skin on my legs, the largest is on the back of my right lower leg.but there are smaller patches on both legs.no pain/itch?

Could be: Dry skin or eczema . You have a lot of allergies so eczema would be a definite possibility . Try over the counter Hydrocortisone cream but this is very weak and you will probably need a prescription , as it won't work any better than a moisturizer but it's worth a try!

Need more info: Skin patches come in many colors, size and shapes. They can also be changing their color and size over time as you observe them. All these historical bits of information help doctors to narrow down the diagnosis to the one that is most likely and advise you about the next steps. You can either provide all of the above (and we can try to guess!) or should go see your doctor(pcp is a good start)

It is possible to be: Many things, something related to blood disorder or rash of some kind, i need more information before we could decided.