You need to see your doctor right away.   We cannot diagnose a condition on this Web site. It isn't clear what caused the reaction all over your body.   Benadryl is an anti-histamine, which is used to block the chemical histamine that is relaesed during an allergic reaction (it's what leads to the itchy, sneezing, etc.). But, in your case, the Benadryl has no effect, which could indicate that the condition is not an allergic reaction, but it could be. You must see a doctor right away and explain the origin of the problem and what you've taken or done to remedy it in the mean time.   Best of luck and good health!