Hello and welcome to the board,
Sometimes runners, and others, think they have pulled a hamstring when in reality they are having an issue with one or more of their lurabar discs, often L4 or L5. Often when a disc herniates there is no back pain involved. The symptoms are often felt along the course of the nerve which in this case runs along part of the buttocks and down the back of the leg. It can stop there or it can run all the way on down into the foot, even to the toes. Sometimes even when there is a minor problem with the disc, if there is any inflammation, it presses on the nerve root and the pain is felt in the back of the thigh. Sometimes ice on the lower back, and rest will take away the inflammation enough that the tissue moves off the nerve and the pain goes away. Other times it may linger for weeks and then resolve, or linger and get worse when the disc ruptures.
But you may have pulled your hamstring and perhaps you are using slightly different body mechanics as a result of the injury. This could throw some of the other muscles and ligaments off-balance, and may be causing some strain on the SI joint, or even in your lower back, resulting in the pain you're feeling in your lower back.
In case it is a disc, I would suggest that you take it easy while you're healing the hamstring--avoid activities that involve bending, twisting and avoid lifting anything heavier than about 10 pounRAB. If you feel you've given it about the amount of time it would take your hamstring to heal and you are still having pain, I would suggest you get a MRI to see if you have something going on in your lower back.
