I have a knot in the lower right side of my back that i've had awhile, it starts to hurt extremely bad if i put pressure on it like when bending down?

Muscular v disc: This is either muscular issue if only several weeks. If longer, it may be from a disc issue that could be a tear in the disc or a herniation. If muscular, it will get better by about 6-8 weeks and 90% of discs improve over time. Otc meds can help as can heat &/or ice as well as guided exercise & activity modification. Lifestyle changes like weight control, not smoking & regular exercise are key.

Many causes: The most frequent one is small fatty tumor get inflamed usually dose not hearts unless get infected. The second possibility is a sebaceous cyst is a closed sac under the skin filled with a cheese-like or oily material also it heart if got infected. Very rear kind is dermoid cyst cold be the problem. Epidermis cyst another possibility.