What is the best treatment for lower back strain? rest seems to help the most.

NSAIDs, stretching: low back pain is a common problem. While disc disease and degeneration often is seen on x Rays, muscle is still the most common reason for continues pain. Therefore, anti inflammatories and muscle relaxants are good medicine choices. Stretching, massage, and strengthening will help. Learning proper ergonomics will prevent recurrences. PT can help.

Back Strain: Low back pain is a fact of life. Just about everybody will suffer from it sooner or later. One of the main causes of back pain, whether acute or chronic, is low back strain. http://www.webmd.com/back-pain/guide/low-back-strain

Exactly: Rest and giving it time to heal is the simplest way to get better. If it does not respond, things like physical therapy can sometimes be the next step.