My son is 17 and got Poison oak about two weeks ago it kinda went away for a couple of days and now its back. He has it on his face , back,neck,arms ,legs and chest. we have tryed ebsensalts wash Benaderal cream,Calamine lotion and Allergy Medicine with Diphenhydramine HCI 25mg. But it is not going away is there anything else we can do ?