I have a medium sized hard lump under my skin on forarm by the inside of elbow it seems to be just getting bigger and more painful i had this for over year what could be?

Lipoma: Lipomas are benign, slow-growing tumors that develop from fat cells. They are usually soft and movable, and can range in size from a small pea to a large grapefruit. Lipomas are not typically painful, but they can become uncomfortable if they grow too large or press on nerves or other structures.

Ganglion cyst: Ganglion cysts are fluid-filled sacs that develop on the tendons or joints of the wrist, hand, or foot. They are usually firm and immovable, and can range in size from a small pea to a large grape. Ganglion cysts can be painful, especially if they put pressure on nerves or other structures.

Ulnar nerve entrapment: Ulnar nerve entrapment occurs when the ulnar nerve, which runs from the neck to the hand, becomes compressed or pinched. This can cause pain, numbness, and tingling in the elbow, forearm, and hand. Ulnar nerve entrapment can be caused by a variety of factors, including trauma, inflammation, and anatomical abnormalities.

Tendonitis: Tendonitis is inflammation of a tendon, which is a tough band of tissue that connects muscle to bone. Tendonitis can be caused by overuse, injury, or certain medical conditions. It can cause pain, swelling, and tenderness in the affected area.

Muscle strain: A muscle strain is a tear or injury to a muscle. Muscle strains can be caused by overuse, injury, or certain medical conditions. They can cause pain, swelling, and weakness in the affected area.

Fracture: A fracture is a break in a bone. Fractures can be caused by trauma, such as a fall or a blow to the body. They can also be caused by certain medical conditions, such as osteoporosis. Fractures can cause pain, swelling, bruising, and deformity.

If you have a lump under your skin that is getting bigger and more painful, it is important to see a doctor to get a diagnosis and appropriate treatment. The doctor may order imaging tests, such as an X-ray or MRI, to determine the cause of the lump.