Random Stabbing Pain Above Left Knee?

I’ve read similar notes on this, but none with my exact symptoms. I have random “stabbing” pains in my left leg just above the knee. They come on without warning, and last less than 30 seconds. But, boy, they seem like they will never stop, since the pain is so excruciating. It happens maybe 3 or 4 times a day. But last night it happened twice. One time waking me screaming out of a deep sleep. I work in a warehouse, but most of my lifting is from a standing position. And the weight is mostly 35 lbs. or less. And oddly, the random pain seems to only come when the leg/knee is inactive. Please Help!