I've been having back pain off and on for the last two months. Just in the last two weeks, it's starting to go into my buttock and down my left leg. How long should I wait to see if it might clear up on its own?
The fact that you've already had some general low back pain for two months suggests the problem is ongoing. We would consider that a yellow (warning) flag. The onset of these new symptoms in the last two weeks is really the red flag to suggest some kind of evaluation is needed.

For most nonspecific low back pain, two months is enough time to recover and return to your full schedule of activities. Research supports staying active and working through back pain. For back problems that don't go away with this approach, early diagnosis and treatment is advised.

Back pain that travels down the leg is called sciatica. This is a sign that something is impinging or pressing on one of the five spinal nerves that form the sciatic nerve. It could be a bulging or herniated disc, bone spur, or tumor. An MRI is needed to sort out the actual cause.

Whenever possible, doctors try to help patients avoid developing chronic pain. That's usually defined as pain that lasts more than three months. You are approaching that time frame now. Getting a medical exam now would be a good idea to help prevent becoming a chronic pain patient and to move along in your rehab process.