There is no pain quite like back pain. It seems unrelenting, and sometimes is, if you do not seek the proper therapy and/or medical attention. Your back is a complex network of nerve fibers and spinal discs that are intricately wired together to support your entire body. If even the little thing goes out of whack, say you stretch a muscle wrong or pinch a nerve; you can wind up with debilitating pain. It might be more serious, like a herniated disc, rupture or disc slippage. If that is the case, you will probably require more stringent therapy than just exercises, perhaps even surgery. If your doctor recommends it, you can seek relief through pain medication, swim therapy or safe exercises.
Stretching is the recommended course for relieving minor back pain; it is non-invasive, no medication is required and it is not too jarring for your spine. Get a proper exercise mat, and attempt one or more of these exercises (you might want to look for some videos with back stretches/exercises to get you started).
Some simple exercises/stretches include the following: 1) you can perform while sitting, standup or lying down. You breathe in, pulling your abdominal muscles back towards your spine, holding in for as long as is comfortable and breathing naturally, up to a minute. 2) a good floor stretch is to press your back towards the mat (if it is not uncomfortable) and gently relax, breathing slowly in and out, keeping your back pressed to the mat with your knees slightly bent. As you become more accustomed to this stretch, you can gradually work your legs towards being flat on the mat.
Another exercise stretch is to lie flat on the mat with knees bent at a 45 degree angle. Slowly raise one leg, while supporting your knee with your hands behind it, clasped behind your upper thigh at the knee crease. Gently stretch your leg towards your chest and hold for two beats, and then go back to the original position, with both feet on the floor. Relax for a few beats, and then repeat with the other leg. One more exercise is to lie on your belly with your hands placed at chest level, elbows in the air, palms flat on the mat. Slowly raise your upper body with your arm strength, stretching your abdominal muscles. If this is at ALL uncomfortable, stop and choose another exercise.
One more exercise is to lie flat on the mat with your arms relaxed to your sides. Gently roll one leg over the other, letting your hips do the work. Stretch that side of your body for two-four seconds, then return to the starting position, resting for a beat or two. Then repeat with the other side.
As with all the exercises here, if you have pain that is too much to bear or feel like you are taxing yourself too much, then stop.
Practice each of these exercises 6-8x/day.