4 months post op & itching/ burning during exercise in treated area (mini TT & Smart Lipo in abs and flanks). Advice?

Even though you are four months post op, there is still healing going on. Your symptoms should improve over the next few months. Your surgeon is right- try to give it more time.

Burning or itching sensations in the abdominal region following a tummy tuck and lipo is the norm rather than the exception. As nerves that were severed during surgery heal, pain is sometimes experienced in the form of burning, and itching. As your DR advised, this will diminish with time.
Your PS may recommend Advil or Neurotin to reduce inflammation. You are wise to return to your normal exercise routine gradually as you listen to your body to not overexert yourself.

Thanks for your question.
Sorry to hear that you are having issues following your surgery.  Itching following surgery is a very common issue.  It is the result of both mechanical stress and chemicals secreted as part of the wound healing process that activate the nerves associated with itching.  The good news is that it almost always goes away with time.  It can take several months to be completely resolved.
In the mean time there are several things you can try to help with the symptoms.  An oral anti-histamine such as Zyrtec or Benadryl is a good start.  Additionally, use of a cold compress or ice has worked for a number of patients as well.  One patient went so far as to use cryotherapy sessions for relief.  Topical creams such as Cortisone usually make a minimal difference.  In very rare and severe cases I have used Neurontin with some success as well.  
Make sure you follow up with your surgeon and discuss the problems you are having.
Best wishes.