The system says that you have requested a new expert.
Actually, CFS, fibromyalgia, and IBS are thought to be similar conditions that are related to excessive sensitivity of the nervous system. There is a large amount of overlap in symptoms, so it is not surprising that someone has been diagnosed with each condition at various times, depending upon which symptom is causing the greatest difficulty.
With the quivering of the stomach and limbs that is persistent despite Bentyl and clonazepam, the usual next medicine that I would try would be an antidepressant. Even when there is no depression, antidepressants may help to ease symptoms related to IBS, fibromyalgia, and CFS, as well as many chronic pain syndromes. There are a number of different antidepressants that can be tried. The most studied is amitriptyline, but we generally try to avoid amitriptyline in someone over age 65. Either an SSRI, such as sertraline or citalopram, or an SNRI, such as venlafaxine or duloxetine, would be preferred.
If I can provide any additional information, please let me know.