Is it right in the center of your back? Or does the pain shoot down one leg? You can relax your back by lying on the floor with your knees bent and the small of your back pressed into the floor. You could do some gentle crunches if it doesn't hurt - strengthening the abdominal muscles helps support the back.
You could try chiropractic if the alignment is off. Massage is good but it won't hold if the alignment is off. If you do chiropractic, I suggest applied kinesiology - more gentle manipulation rather than the "cracking" or snapping that I think much research shows to be dangerous. When you have an injury, you want to apply ice first for 24 hours to reduce inflammation, then do heat. Some people do it in reverse - the heat feels good but it increases the inflammation.
I've used nutritional supplementation for sciatic back pain, and both my husband and son are athletes who do a lot with muscle strains and joint issues. They are now pain free, as am I. We use a comprehensive joint formula (patented so it's the only one out there like it) and a muscle repair/recovery product. After years of using health food store products with no results, we've found what works. That's a route you haven't tried and you might want to consider it.