I'm a lifetime back pain sufferer. In my experience, it is mostly due to lack of exercise and it sounds like you might even have sprain your back (yep, that's possible and I've had that happen to me twice). No medicine will get your back to normal, it just kills the pain and it is the fact that you move that will bring things back to normal unless something is really out of whack. There are a few things that really work for me:
Have you tried Robaxacet? (If that's available in your area)
Hot compresses to relax the muscles, stretch for 10 to 20 minutes, then ice inside a towel (ice should never touch the skin directly) to lower the pain level.
Stretches: (you will probably not be able to do all of these or just to a limited degree at first. Stick with what you can do and stop the movement to the point before it becomes painful... or TOO painful in your case):
The leg "wiper" movement is a great start, I don't understand why it's not one of the very first stretches in the video.
Pulling both knees towards your chest (like in a fetus position while lying on your back) and keeping it there as long as possible is one of the best stretches for me when the pain is really bad.
Also:
7 Best Yoga Poses to Soothe Back Pain - Back Pain Center - Everyday Health
The one with the ankle over the knee and pulling on the knee is also a great start most of the time. Just stop the movement at the point where you are comfortable.
I try to do all of these movements as often as possible (2-3 times a day when I'm really suffering) and after a while I can really tell my back is doing much better. Hope this helps...