Thank you for your query,
Normally hydrogen peroxide
always “ foamed” if get in contact with any skin lesion and not necessarily that side still contain poison. From your description seems to be allergic reaction
if you have rash and itchy. You must use antihistaminies tablets ( one of them) like Dephenhydramine, Cetirizine
, plus local lotions like calamine lotion. All these medication you can get over the counter and pharmacist will explain you details. Be carefully when you driving while use antihistamines. If after few days will be no improvement after this treatment then you need consult your Doctor who can prescribe you corticosteroids
I wish you speedy recovery.