If a stretch seems to make things worse, or if it causes pain to go down your leg, stop for a while. There's nothing wrong with trying heat if it works, but ice may be better. Medications may be prescribed by your doctor. It's much more effective to take them regularly as opposed to only when you hurt. Start with about 5 - 10 minutes of exercise a day, three days a week, and gradually work up to 30 minutes of exercise a day for five days a week.
Any exercise is better than none.
If you are not getting better, manipulation or a special stretching program called McKenzie exercises may be recommended by your doctor. Participating regularly in an exercise program will help your back, plus it will help keep you healthier overall. When lifting a heavy object keep the object close to your body. Avoid sitting in one place or in one position for a long time. Get up and stretch, walk about and change positions.