Everytime I sit down for a while my knee and elbow hurts really bad and I have to stretch them...What could be the reason and possible solution?

Stiffness . Discomfort during rest after activity is typically related to inflammation or stiffness of a joint. Stiffness is the hallmark of joint degeneration, often being osteoarthritis. Inflammation can occur in the joint itself or in the soft tissues around the joint. Treatment depends on the cause. An exam by a doctor and x-rays can reveal the source. Treatment can include pt, meds, injections, etc.