Left leg pain very sore feels tired and numb all the time please help!?

Hello can any help i have been having problems in my left leg it feels tired all the hurts to bend like when i sit on the couch and put the left leg under me can't do it.the other day my left leg gave out on me and i fell down. i got hurt back in January from work i slipped and fell on ice and hit my left knee ever since then i have been having a lot of problems with this leg. i lost my job from it and plus i was on workman comp which i am no longer on but i do have a lawyer. but every time i get up my left leg is always sore fells tired and numb all the time i can't stand on it very long without it hurting. would anyone know what it is? please help i think i have a very serious problem on my hands it gets to the point where it feels like it's starting to swell. just need the pain to go away keeps me up at night thanks again