440 grams of carbohydrates/serving for the vanilla...

I can't find a label...to see what kind of sugar has in it.
Sucrose is easier on people than fructose.
There are two types of fructose intolerance..
one is GI mostly, the other is a liver reaction (genetic).

Also you need to look at magnesium content. Some shakes have high magnesium added and this can cause diarrhea in some people.

You might try simple Whey protein...with no added sugar.
Adding the flax oil is great.

I have never been able to drink apple juice like others...so I think I have had this forever, and it just became acute when I was ill. I seem to be able to eat some cereals, but not others. Plain oatmeal is okay for me, but not the flavored instant type (lots of sugars in them).
At one point last year my doctor had me have abdominal ultrasound thinking I had gall bladder problems...it was horrible gas/pain every day...but all was negative.
I was so surprised when I cut out all fructose...it was amazing the CHANGE!

Long term use of drugs like Protonix (proton pump inhibitors) can mess up absorption of some nutrients:
B12
folic acid
calcium
magnesium
zinc
iron.

Those drugs also prevent protein digestion, which leads to bacterial fermentation in the bowel by bacteria, and the subsequent gas and diarrhea. Short term use is okay, but the way that doctors hand them out "for life" with no supervision, is just terrible IMO.

You can PM me anytime, if you have other questions. I don't often get to this forum commonly