What could be causing sudden new symptom of weak and burning, aching muscles in my legs?

[chilove]

Looking for suggestions on what could be causing a recent and sudden new symptom: Aching and burning and sore muscles in my legs? It started with my left knee suddenly giving out while I was walking but it didn't hurt, my knee would just sort of buckle. Then it progressed to that knee getting very swollen then it started hurting. Now my right thigh is also hurting and it feels inflammed inside but is not visibly swollen like the left knee is.

I do have MCAS and histamine issues and I have been eating more high histamine foods than I should lately due to stress. I wonder if that could be causing this?