I have what appears to be a small lump of the right side of my thoracic cavity. i have had the same thing 3 other times. is this a disease?

Lumps on chest: I am assuming your lump is on the outside of the chest wall (not internal and detected by a ct scan). The most common cause of external lumps over the rib cage are lipomas -- benign fatty tissues. They do not tend to go away by themselves, but generally do no harm. Other causes are mostly cysts--either cysts of the skin or sebaceous cysts.

Hard to know: There are several possible causes for what you describe, including cysts, lipomas, lymph nodes, and others.