The disc does not have to herniate for it to cause pain. Sometimes it can slightly bulge forward or backward from in-between the vertebrae. This bulge would press on structures in the area and cause pain.
If your disc has not yet herniated and has only started to bulge out, physical therapy can be extremely helpful. Physical therapists have techniques that can help get rid of the bulge. This will, in turn, get rid of your pain. They will also teach you how to manage your own back pain so that if the same symptoms were to occur again, you would know what to do. A physical therapist will teach you exercises and techniques, which will decrease the chance of your back pain returning later.
If you have herniated your disc, quite often you will require a couple of days of bed rest before you can rehabilitate. Some people may even require surgery to get rid of the herniation. A physical therapist can help you after your herniation or surgery by teaching you how to make sure you do not herniate a disc again.