you "did something" to your digestion being a fruitarian, yes. we're not chimpanzees. however, that will heal with a more varied diet and probiotics.
for so many on bad diets, they feel like krap, basically all the time, so it's "normal". once the diet gets cleaned up, it's easier to pinpoint the specific foods that truly make you feel like ass.
if you feel adverse reactions to grains, and clearly you do, -- stop eating them.
As I ate the oysters with their strong taste of the sea and their faint metallic taste that the cold white wine washed away, leaving only the sea taste and the succulent texture, and as I drank their cold liquid from each shell and washed it down with the crisp taste of the wine, I lost the empty feeling and began to be happy and to make plans.
– Ernest Hemingway