Tegretol doseage and long term results

I am a long term victim of tn. I am 69 and started with the affliction in my early fifties. I have had two mvd, two alcohol injections ,two glycerol injections and one gamma knife(radiation) procedure. After my second mvd I was pain and med free for eleven years. Now, I have started back up with pain on the other side of my face. The neurology doctor stated that Only 1% of tn patients have pain on both side of their face. I guess I am lucky in the fact that only one side goes off at a time. I am now on 3 200mg of Tegretol per day. This is keeping me mostly pain free. My question- Does Tegretol build up immunity over time and become less effective. Also, is there anything that can prevent the drowiness that comes with tegretol. Outside of this affliction, I am a very healthy man so I dearly hope the meds work for me. I would dearly hope to hear from other tn patients who have used Tegretol.