Hello Grace, please bear in mind that I'm not a doctor or a health professional, and neither are any of the others posting here, so keep those grains of salt handy!
I have heard of rashes as a side effect of some medications when you are taking them, but not as a withdrawal effect. I have had some nasty side effects inc oming off some medications, brain zaps, feeling spacy, that kind of thing. In those cases, my doctor changed my tapering off plan. Some drugs need to be tapered off at a glacial pace to avoid symptoms.
I would look up the consumer medicine information on the internet associated with whatever it is you've been taking, they are required by law to list all the known side effects associated with the drug. Get a second opinion from another GP if you feel unsure. I would have thought, at the very least, the doctor would give you an idea of what the rash is caused by (rather than what it isn't) and a prognosis or treatment plan for clearing it up.
