Sounds to me like he's literally "Worrying himself sick". If RR doesn't seem to make much of a difference, you could also try the ThunderShirt. He needs to learn to not just settle but relax.
Something you could try for him, may not make much of a difference, but you could take his food and stuff it in a dispensing you. With wet foods, you can fill a few classic rubber Kong's and place them in the freezer, and replace one of his bowl meals with a frozen Kong game instead.
And how many times does he get to go out a day/week with the family for a nice relaxing long walk? I'd suggest a later in the day long walk, maybe go to a new place, and get him a little more tired out before bed.
And last but not least, have you before, and are you now giving him any meds for his stomach problems? Were they an "antacid"? He may want to eat more, because his stomach is to acidic right now, which could be caused by the anxiety he's having. I'd ask the vet about what to try for an antacid, but most usually suggest to start with Tums, Just make sure to read the bottle first and avoid anything with artificial sweeteners! They're becoming very popular in meds these days, and most if not all are toxic to pets.