I also suffer from muscle spasms in my back due to herniated discs that damaged nerve roots at my spinal column. I can completely sympathize with what you're going through. In fact, my entire second semester of pregnancy with my second child was spent on bed-rest and percocet due to a muscle spasm. I was on crutches and crawling when I absolutely had to be out of bed to go to the bathroom or to physical therapy.
I will say that physical therapy helped enormously. It's more focused than massage therapy but similar. The therapist was able to work deep into the muscle that was seized up and get it to release a little more with every session. It hurt like the dickens, but not as bad as the spasm itself!
What I do now is actually "preventive" self-treatment that I worked out with my doctor. I always have 800mg ibuprofen and flexeril (muscle relaxers) with me in case I feel one coming on (you know how you can tell that you're getting one..). Anyways, when I feel one coming on I immediately take a break from whatever I'm doing, even if I have to spend a couple of days doing mostly nothing but the bare necessities, I take the flexeril three times per day and the ibuprofen too (since mine is from irritated nerves the ibuprofen helps reduce swelling that's pressing on them), I lay down as much as possible and I also use a little inversion therapy. Of course, mine is worse with standing and downward pressure because of the nature of my injury, so hanging upside down or even laying upside down on a sloping chaise helps me a ton, but it might not help you if your injury is of a different nature. You just have to find what works for you as far as reducing the pressure on the injury that is causing your spasm. Stretching helps too, but you have to do yoga style stretching that is longer and more intensive than regular stretching.
The important thing is to pay attention to your body and take preventive measures BEFORE it gets it's teeth into you. They are so much easier to prevent than to cure.
That's all I can think of now but feel free to message me any time you need to commisserate with another muscle spasm sufferer. Most people have no concept of how excruciating they are. I know that it's like a major labor contraction, but it's all of the muscles of my back and hips and it doesn't go away for weeks at a time. I've been there and I can empathize. I'm so sorry you have to deal with this. I hope things get resolved for you soon.