Twitching/muscle spasms and numbness after genioplasty. Why does this happen?

Hello, I underwent genioplasty on 27/12/2013 to correct an asymmetrical chin, I had a T-cut genioplasty. Picture attached. On the 3rd week, my left chin started constantly twitching/spasms, it starting to shift slowly to the left by itself and move back into position in the center. This is my 5th week, the twitching/spasms are not that frequent, but it does happens once in a while, why does this happen? I have uneven swelling, my left side made a faster recovery than my right side, I still have swelling and numbness on my right side, can someone please explain why uneven swelling happens?

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