Consistent Diarrhea

About 3 weeks ago my dood threw up a little bit and began immediately, like a light switch, having consistent diarrhea. There were zero changes to his diet or new packages of anything he eats recebtly. He's on a pretty regimented diet of time and type. No puking after the one time so maybe unrelated and just coincidence. He's acting completely normal. No lose of energy or appetite. First visit to the vet they put him on I/D, FortaFlora and Metronidazole. Was told if things don't improve in a few days to bring him back. So I did. They continued him on I/D and Metronidazole but changed the probiotic to proviable. This didn't fix it. They suggested ultrasound and a blood panel. The ultra sound was yesterday and didn't show anything. It actually had some good news as his adrenal gland was previously undersized when he was younger and is now normal. The blood panel, looking for deficiencies, hasn't come back yet. Meanwhile his bowel movements, though diarrhea, which were still normal where he had no eagerness to go, have turned into him whining in the middle of the night or in the early morning to go outside because he had to go. Vet suggested, if the blood panel doesn't turn up anything, that they refer him to a specialist (I don't remember what type exactly). Anyway, I thought I'd come pick the reddit brain and see if anything comes up similarly for anyone's dood. Any thoughts? Again, he's acting normal but making a bowel movement has become a bit more urgent for him which now has me a bit more concerned for his own comfort.

UPDATE: This is months past but I thought I'd update in case it helps anyone. My dood developed a new allergy for all protein. He's been on a hydrolyzed diet for months and has perfect poops and minimal scratching.