HI Shawna, and welcome to the forum,
There is hereditary form of mastocytosis, and researchers are also studying mast cell dysfunction in fibromyalgia patients. They now feel there's a connection.
Many people with mast cell disorders have digestive problems, and it's known that mast cells can be the culprit. When your son has his testing, you might ask them to test for mast cells,too, and, if they find he has too many in his digestive system, to do a morphology on them. Gastrocrom is the treatment of choice for that problem. 6-8 weeks of gastrocrom might give a long term positive result, or treatment may need to be ongoing. I've also had a lot of luck using probiotics. My favorite at the moment is "Align," which is available over the counter at pharmacies.
If you haven't already, you might want to try a low histamine diet for both of you. (
www.urticaria.thunderworksinc.com/pages/lowhistamine.htm) You do have to be strict on it, because eating just one high histamine food or a food that triggers direct histamine release can send you back to square one.
Regarding doxepin, I took it in the beginning just to get some relief from the symptoms. However, I only took 10 mg. and only in the evening before bed. It helped my sleep, and I felt rested in the morning. Of course, we're all different and that may not be the best med for you.