Hi,
sorry you got these symptoms back. I also had the burnt sensation and numbness before my surgery. It disappeared a few days after surgery, and then came back with a vengeance after about 2 months. I contacted my neurosurgeon and he said that fluctuations such as this are not uncommon for the sensory nerves (the trigeminal nerve in this case) and that it is hard to say if they are due to some permanent damage. He said there is no "solution" and I just have to wait it out. Fortunately for me, the numbness and burnt sensations started to improve gradually, until they completely disappeared and now everything is back to normal.
You are further off from surgery than I am, but I suppose that these fluctuations can still happen. Since your doctor does not see an obvious reason from the MRI, I would wait it out. Remember, nerves are so sensitive, as they regenerate all sorts of rewiring and strange things happen.
Marianna