Only your doctor can give you the correct diagnosis. Possible causes It may have been triggered by a small local injury that you hardly noticed at the time or have long forgotten about. Finally there are much rarer causes of bone, joint or muscle pain - such as infections and tumours. This condition is an inflammation of a tendon where it attaches to one of the bony lumps at the outer side of the elbow. Treatment involves regular painkillers.
Rest is important, and local strapping or devices to take the pressure off the tendon can also help.
If pain persists, your doctor may be able to give you an injection of steroids into the tendon which can bring rapid pain relief. No sport here, but a good book can cause you to lean overlong on your elbows, causing a traumatic bursitis or inflammation of the bursa behind the elbow. This bursa or sack of fluid becomes swollen and painful. Infection and gout can have the same effect. Treatment involves draining out the fluid and, if it is a traumatic bursitis, a steroid injection.