If it's not an allergy it could be too high a dose. I had that sensation when I took a lot at once. Another reason to ask your doctor how to deal with this. You don't want to take more than you absolutely need and definitely don't want to take an allergen daily, if that's the cause.
I agree with Nurse girl I have never heard of this reaction and have help a lot of people with methadone call the doctor............Gnarly
You need to notify your doctor. You could be having an allergic reaction. Some opiates cause itching, but you report that it's severe. Sort it out with the doc who Rx'es the Methadone to you.
Good luck!