hi mad4, you sound very much like me, I was thinking in all directions and following various avenues but in the end for us it came together, hope it does for you too, eventually..
The cameras and all the macro-stuff mainly look at macro problems, eg structural damage, occasionally miscroscopic if they take the samples to view under the microscope. But they don't look at biochemistry a lot of which is dynamic and depends on nutrition.
Anyone correct me if I am wrong, but camera work is not likely pick up allergies. When I started on my ds problems, I listed absolutely all signs of anything weird/different and tried to look for links.
Have a look at the link stuff below, which explains well how intolerances originate and build-up and how you can work to unravel all this.
Bananas are predominantly carbs, carbs are digested mostly by pancreas enzymes. Maybe he is taking in too much carbs and overloading his pancreas? My ds had a similar test to vega but apart from intolerances, he came up deficient for various nutrients & vitamins. Did the test pick up any deficiencies for your ds? My ds had aminoacid deficiencies and he at the time was vegeterian, but none of over the counter aminoacids were found suitable to supplement.
When they are little they do need proteins and he was living mainly on carbs. We had to go gluten-free and also slowly introduce proteins in soups/caseroles etc.
The link below is not specifically about babies, but I think it describes the allergenic process really well. Whilst that one is mainly about wheat, it does talk about other allergens too, like corn, citrus etc. Maybe it helps you to see a bigger picture.
link