There is the possibility from your description that you may be having radiculopathy (pain caused by compression of the nerves in the low back leading to radiating pain down your leg in the same distribution as the nerve). The sharp shooting pain is a classic description of the type of pain associated with radiculpathy. Pressure on the nerve can be from anywhere along the length of the nerve, but usually occurs as it exits the spinal canal through the foramen (small opening on the side of the spine where the nerve exits from).
Degenerative changes are usually the cause of compression, mostly from disc herniations but also from slippage of the bones in the spine. Other possibilities include hip or knee pathology. One way to test for this is to palpate over your hip and knee, and also assess whether you have good range of motion in both joints without pain. Regardless, it is important that you are evaluated by your primary care doctor
who will be best able to assess your presenting symptoms and medical history and decide upon the appropriate work up. This may include imaging studies or a referral to a specialist.