Started 2 days ago - sporadic, sudden burning on back even if just sitting, severe like on fire but not painful - not like normal hot flashes.

Many possibilities: Considering the symptoms you describe, there are a number of possibilities that could be causing your back pain, which could include muscle strain/sprain, nerve impingement, shingles, etc. It is best for you to be examined by a doctor to determine the specific cause. Best wishes.

See doctor : Severe burning sounds like a type of severe pain to me. That is not normal. You should be seen by a doctor for a good physical exam.