Allergic to running??

Have any of you heard of urticaria? I have been experiencing intense hives all over my body after running recently. Nothing had changed as far as my diet or laundry detergent. The research i've done said you can literally be allergic to running and a lot of people experience this. The hives go away with benadryl. But I have a marathon to train for and cannot be having this! Any thoughts? Or do any of you guys suffer from this also?