Hi Poco,
Oh, I can sooo relate to your back, neck pain, spasms. I'm dealing with that right now too. My pain is in my neck (arthritis), and in my lower back (sacroiliitis), right shoulder, and both feet. I get the spasms in my mid back too. So bad they literally take my breath away.
My guess, is that you've been referred to a rheumatologist so that they can investigate if this is a rheumatic condition you have like rheumatoid arthritis, general arthritis or something called Ankylosing Spondylitis. Google that crazy set of words, LOL.
It's something that I'm looking at right now. I have all the symptoms except the positive antibody test. Your symptoms and pain sound a lot like mine. By any chance do you have foot, heel, toe or ankle pain? Trouble walking? Any pain in your shoulders? Oh, yep I just re-read your post. Shoulder blades. Bowel issues are very common in AS, as you'll read about. It's from the fusing of the bones which cause the nerves to your bowels, and for some people the bladder, to not function properly. Here's a link to a good AS site.
http://www.spondylitis.org/about/as.aspx
I'd take a peak at the AS possibility. But don't try to self diagnose. Just use this as a tool to further your knowledge and understanding. Something to ask the rheumy about.
Keep us updated on your appointment. If you have any questions, just ask. A lot of us have back, neck pain issues. It's exhausting to live with. I'm at my wits end... I can understand your pain and frustration with this.
Keep pluggin' along,
Ginny