I can’t help with diagnosis but wonder if any of this might help.
Is there edema in your legs? If so, try sleeping with your legs raised and see if it helps. Even if you are a side sleeper try on your back with legs propped up a bit. It might give you an indication if it is related to blood vessels.
I always thought that you get to sit in a rocking chair when you get old. No way. Sitting is what kills you. Move your legs once an hour at least. Even if you feel pain, keep moving.