my son is 11 yrs old. He started with what looked like an allergic reaction to poison sumac on his forearms and calves. Very blistered, oozing and painful. That lasted 3 weeks and is almost resolved but now presents with a fine, red, itchy rash on his cheeks and one ear lobe. What could it be? He doesn't have any other symptoms. We have treated with cortizone cream and Zyrtec but no relief.