Lately I've been getting these rashes that appears on my face arms upper torso and leggs. It's very red and burns like a sunburn. I have to take a antihistamine. It goes right away after I take the pill. I can't figure out what causes it.

Does it happen at any particular time of day, or in any particular place? If it appears suddenly and goes away quickly with antihistamine, it probably is an allergy.

Why don't you try a journal of when it happens and under what circumstances, to help you solve the mystery?