I Fell Down And Hit My Knees. The Left Knee

I fell down and hit my knees. The left knee is tender to the touch in the middle right below the knee cap. Behind my knee is now bothering me by a dull constant ache when I am sitting down more than standing up. It also is causing an ache up the hamstring area like when I used to have what I called Sciatic pain that ran all the way up the back of my leg.