hello You may see an orthopedist for checkup, if MRI is necessary, it would be advised.In meantime do hot fomentation and take OTC advil tabs thrice a day after meals and apply anti-inflammatory gel or muscle relaxant gel after fomentation.Pain and stiffness in knee is common with osteoarthritis, a degenerative disease wherein the cartilage and ends of bones forming the joint gradually loose connective tissue and loss of trabecular pattern of bone leading to lysis of bone ends and gradual destruction of bone. This leads to cartilage pressure on weight bearing excessively and further degeneration occurs into the joint.there may be effussion, narrowing of joint space leading to stiffness.The surrounding muscles go into protective spasm and therefore stiffness.Some doctors prefer to add muscle relaxant tabs orally, while few advise inj hydrocortisone into the joint.Hyaluronidase is another good injection to relieve pain.In intractable cases, when joint is grossly destroyed, knee replacement is advised. So consultation with an orthopedist is must thanks