I fell out of bed weeks ago and hit my left knee on the hard floor. Now weeks later the area is tender and the lowr leg is swollen tender and itches?

Blood clot. You need to have the leg examined for a possible deep or superficial vein clot. A ruptured baker's cyst or a knee effusion are other possible causes. It needs an exam and possibly xrays and/or ultrasound to sort this out.