Sharp stabbing pain above my left knee. hurts more when my knee is in flexion( sitting or sleeping ). what is going on?

Quad strain?: Difficult to say w/out examination but sounds like you may have strained your quadriceps muscle or quads tendon w/ symptoms u are describing. Best to have it checked out so see your pcp w/ referral to orthopedist if necessary. Best of luck!

What is tender?: Best clues the body gives is: what is tender to touch causes most of the pain. If the joint moves well and without pain, then the problem is most likely from muscle and fascia. A tender muscle knot, part of a ropey band of muscle, is a trigger point and the pain is myofascial. Beyond this you might need to be examined. www.blatmanhealthandwellness.com.