In my part of the world, Hywel Dda, you an self refer to an NHS physiotherapist. It might take a while before you are seen, but you don’t have to go through a GP. It is probably worth seeing your GP as well.
@Pete2 Go to your doctor. Once I did that with a bad back. I explained that I had foolishly carried an oxygen cylinder. He asked, “Do you want a certificate?”. “No, I want to be cured!”. Only then did he examine me. I got some kind of embrocation and my back got better, but do stress to your doctor that it is a cure you want!
Self refer to physio if you can. It sounds like you’ve just carried too much on a small area. If it feels like sciatica then there’s a bit of nerve involvement. I suspect you’ve tired your traps out so much they gotten really tight. Hard to say without seeing you.
If you don’t mind paying privately, then that’s a very quick way to be seen.