Debby, I almost fell out of my chair when you mentioned gluten-free!!!
Right before all of this started, my hubbie and I read a book called Wheat Belly, which is by a preventive cardiologist. The book made a compelling case (not only against wheat, but all grains), and my husband and I both attempted to go gluten-free, and largely grain-free.
My sister (who also did this at the same time and has had lifelong trouble with constipation) raved about how much better her bathroom habits were after doing this, and my husband (who has IBS) had improved bathroom time, too. I couldn't figure out what I was doing wrong!
Both DH and I cut down to eating gluten maybe once a week, and right after that is when all of these symptoms started--markedly worse constipation (I hear ya on the rabbit pellets, sister!), the lymph node swelling, and after about two months, these fibro-type symptoms.
I had thought about the timing of all this before, but couldn't imagine a connection to the mostly-gluten-free diet I was trying, but now you've made me wonder. Like I said, I was prone to constipation before, but this was far beyond anything I'd ever experienced...at one point I didn't "go" for almost three weeks!! That's when I went to the gastroenterologist.
Now I'm really wondering how to proceed. I had told my husband before that I was considering going back to my grain-laden diet. One of my main reasons for trying to exclude gluten from my diet is because I have osteopenia, and grain makes a person's system very acidic, and your body tries to neutralize this with calcium from your bones.
Well, you have given me a lot of food for thought--pun intended! 
Thank you so much for taking the time to tell me your story, and believe it or not, I appreciate the details!