I'm in Scotland so it might be different but I call up every so often to get an estimate of where DS2 is on the waiting list and how much longer we might be waiting. They have a huge backlog obviously with covid so we've been waiting about 18 months so far and they estimate it'll be his turn in the summer hopefully before he starts nursery in august so still a while to go. With DS1 he was diagnosed just after his 4th birthday and it took less than a year from referral to diagnosis.
Its definitely worth calling to make sure you are still on the list and see if they can give you an update or waiting times.
As for support, honestly, you need to look at some charities for help at the moment. Even after diagnosis, support is pretty weak. Try and find some local groups on facebook for support, and maybe actual groups that you can attend in person when it's all allowed again. Always go to your GP if your DS is struggling with anything in particular like sleep. You can also apply for DLA without a diagnosis, the form can be a bit of a minefield to fill in and I recommend looking up the cerebra DLA guide if you do apply.
If you are struggling personally with mental health or anything then please do go and see your GP. In person support is obviously very limited at the moment but your GP should be able to help in the short term until things are a bit more normal.
Have you got a good support network? Partner, family, friends? Try to accept help from whoever is willing to provide it, even if it is just to have an hour to yourself on a walk or whatever. A short break from it all really can make a huge difference. 