Sorry I am late in responding to this Steph.I have been dealing with my own demons for a few days but anyhow...wanted to say I hope you are feeling much ,much better and that the infection you had has well and truly gone.

Facial tremor? I have noticed this sometimes in myself.Not a major concern for me as yet but I do know how self conscious it could make you feel.Do you notice it at any particular time ie. when you are tired,or in a stressful situation [although kissing would negate that theory ! lol] Then again it depends who you are kissing Brad Pitt...I`d say no problem.
George Bush and I reckon my lips wouldn`t just twitch.They`d implode !!!!
Shrink ! Go on vacation !!!
But...back to serious...I think you are on to something when you say your mouth feels clamped .I find that when I focus on this,I realise I am holding my jaw really tightly.It happens without you realising,and if you are anything like me [which I expect you are glad you are not lol] your jaw has probably been tense for a while,then the quivering starts.
I try to be aware what is happening muscle wise...and then do something about it. If you allow your chin to drop towards your chest...lower your head slightly,this helps to release the tension.This was a tip I picked up from a magazine article relating to tension in the head and neck when driving.
Strangely enough this small adjustment for a few minutes,releases the jaw and the tension should disappear,and then hopefully the tremor in the mouth will ease too.

Hope this helps a little.
Love
Steff
x