Sue, I am sure many people feel as you do, they just hide it.
If it didn't bother you, that would be OK. We are old enough now to please ourselves, and choose what events, if any, we want to attend.
Personally I never go to the official works do now, even thought people try to persuade me. I prefer to go out with people I like.
However you seem to really suffer for some weeks beforehand, and that's not good. I suppose you have to ask yourself, do you actually want to get some help to try and overcome these lifelong feelings, so you can at least be less upset by the festive period?
Or, could you change your mindset a bit, and just accept it's not your favourite time, but it will be over soon. Could you just give yourself a treat or two, and relax and don't bother about what others think.
Many, many people SEEM to be having a wonderful time, but if you really talked honestly to them, you'd find all sorts of issues and problems going on, under the jolly façade.