Lower back pain can be caused by a large variety of factors. Severe lower back pain is commonly associated with skeletal displacement or disk deterioration symptoms. If you are experiencing moderate to severe lower back pain please seek help from a physician. Proceeding physical activity with these symptoms may lead to further injury. Lower back pain is also commonly caused by lack of flexibility, a weak core, and muscular imbalance.
Things to keep in mind
Think of your body as a structure; you need a strong core in order to have a strong body. Your core or foundation includes major and minor muscles such as Abdominals, Obliques, Erector Spinae, Gluteus and so on.
A strong core equals a happy body and a happy back. If your core is not strong enough to support your body, then your back is at greater risk of discomfort and even injury.
Tight muscles including Hamstrings, Quadriceps, Gluteus and others can cause your hips and spine to become unaligned. When the spine becomes unaligned the risk of pinching a nerve or injuring/herniating a disk increases. Injury to your lower back especially between vertabrea L4 & L5 can often lead to Sciatica.
Over development of a muscle or muscle group can also lead to back pain. A common imbalance that causes back pain is one hamstring being more developed then the other hamstring. For example, if your right hamstring is more developed than the left hamstring then your right hamstring can "pull" your back out of alignment.