Have large knot behind knee, calf it's has gotten bigger. leg painful and having muscle cramps.hurts to bend it, stand, lay it on things. what is it?

See MD: Sounds like a Bakers' or politeal cyst most commonly seen secondary to arthritis w/ a degenerative meniscal ( cartilage) tear. Fluid from your knee joint leaks out thru the tear in the cartilage ( and knee capsule) and collects and forms the cyst. Very common; however see your primary care physician to rule out other potential problems( DVT, etc.)best of luck !