I have a lump on the back of my arm under skin on top of elbow tendon and on top of skin above it are a few raised bumps. Been there for months?

Olecranon bursa. This sounds like olecranon on bursitis. This is summer you could confirm with your physician.
Picture ? Skin lesions are so varied that unless seen it's hard to tell. A lump present for months without change, so a slow growing process. One cannot tell exactly without feel or lump and seeing it what it maybe. .