Are there foods that can cause a reaction of red blotches all over the body, itching like cactus prickles?

Sounds like an allergy to me. You need to check with your doctor who will probably send you to an allergist for allergy testing. As long as you are not having respiratory problems/difficulty swallowing or breathing... you can just make an appointment with your doctor. If you have any wheezing/difficulty swallowing/difficulty breathing... get to an ER because when you have an allergic reaction... if it effects your respiratory status, you need epinephrine/benadryl/steroids IV pretty fast before you can't breath at all. Good luck.