That is an excellent question and one that is best answered by your primary care doctor
or other medical professional. In general, there are several causes for low back pain as you describe, but unfortunately it is difficult to know what is causing your pain as there is very little history provided regarding your age, gender, or other medical comorbidities. Regardless, there are several causes of back pain that we can discuss here. Have you had any trauma to your back, as this is a common cause of back pain? Have you performed any heavy lifting, or performed any vigorous exercise which is outside what you normally would do? It is possible that you have mechanical back pain related to stress on the muscles of your lower back, increased weight being placed on your low back if you are obese, or you could have degenerative changes to the bones in your lumbar spine which may cause you to have some of these pains that radiate down into your legs or buttocks. It is best if you are evaluated by your medical professional so he or she can perform tests and get a good history and physical to best elucidate the cause of this.