What Causes Pain In The Legs?

I just started back working after three years , and the job I m doing is constantly on my feet. And after I get of work I can barely walk. I soak in epitome salt and hot water. That helps for a minute. On the way home while driving I can t stretch my left out or sit normal because of the pain I m up crying now because of the pain is so severeI It s my left leg I try use heating pad pain will not stop. It s getting where I can t take it throbbing pain sometimes my foot the back of my knee and it shoot to mt thigh. I know I have sciatica from 27 years working at the VA Medical Center taking care of Veterans. But this is another level of pain 800 motrins not helping me Please what wrong with my leg