I have a stabbing pain once in awhile that starts in the back of my knee and goes to my ankle and heel. It only happens once in awhile and goes away shortly after I relax it, but comes back in the day?

Varied. Could be tight muscles that need stretching, unlikely to be serious, sometimes a low potassium level will cause this.
Tight achilles . Most likely your achilles tendon is tight. You will need daily stretching exercises for your calf muscles. You can learn those exercises by talking to some trainers, your physician, or physical therapists.
Possible muscle spas. Possible muscle spasm in back or disc problem. Have it checked out by your dr.
Leg cramp? Leg cramps are related to electrolyte imbalance, dehydration or strenuous excercise.