What are the causes of pain in the back and down the leg?

A pinched nerve: Decreased space for the nerves in the low back can results in low back pain that radiates into the lower extremities. This can be due to a herniated disc, spinal stenosis, spondylolisthesis, or a variety of other reasons (including hip arthritis, poor circulation, etc.).

Several things : Including a disc herniation. There are other possibilities. Peripheral vascular disease & spinal stenosis both can cause pain into a leg mimicking sciatic pain as can other issues like hip & knee arthritis. Other causes of nerve compression in the spine due to a tumor, infection or fracture can cause this pain. Pyriformis syndrome can also cause radiating leg pain as can sacroiliac joint issues.

Could be your back: It is difficult to answer given the amount of information. Isolated pain on the back of your leg could be from an injury. In the calf it could be from a blood clot. If it runs down the back of your leg it could be your back. It is probably worth getting checked out by a primary care provider.