Rashes keep coming back even i drink anti-histamine and prednisone? What will i do?

Patient: Early in the morning i notice some rashes in my arms and hands then on my butt and legs. Day before the rashes appears i ate peanut butter for my snacks and shrimps for my dinner. I consult a doctor and gave me anti-histamine and prednisone but i wonder after i drink the drugs it subsides for how many hours but after then the rashes will appear again. Its been 3 days now and still the rashes keep coming back. What will i do?