Someone else had a problem with poison oak spreading after treatment.   First, make sure that you're not re-exposing yourself to the poison oak. The oil in the plant's leaves that causes the itching and blistering can remain on clothes and fabric for a long time -- sometimes for months! If you come in contact with the oil again, it can cause new blisters.Try washing the clothes (with soap) you were wearing when you got poison oak. If you had them in a laundry bag, wash that and any clothes there were in there with them too. If you have any pets that were also exposed to the poison oak, give the pet a bath.   It may also take a little while for the rash to go away completely. If you still don't get relief, or the rash and blisters seems to get worse or spread, then contact your doctor right away.