My son has had a rash for months off and on doctor keeps saying its poision oak or ivy they arent sure but we can't seem to get answers.

Many possibilities. Rash is so common, but poison ivy or oak usually does not last that long, and thus you should look for other causes. Detailed information regarding the rash distribution, persistent or intermittent, itchy or not, the age of your son, food allergy, medicine he may be taking, any other symptoms etc are all very important in deciding the cause. Ask the doctor if he can send your son to a dermatologis.