I Fell On My Knee Last Week And The Front

I fell on my knee last week and the front was bruised and scraped, but that wasn't as problematic as I can not lift my foot/leg more than 2 inches off the ground and every time I sit down and have to get up it takes extreme effort but I can walk after I get going. I have a dull ache in the back of my knee. Any idea what could be going on? Thanks.