Why am i having constant pain in my left leg,ankle and foot?

i have been having throbbing,aching,severe pain in my left leg for 11/2 months now.my leg is also restless to.i was to also have total knee replacement 3 to 4 mathshs ago.had acl tranceplant in 2000.what? help it is very painful.i can lay down ,it stops hurting