Mometezuma, are you taking any anti-inflamatory drugs for pain? They can cause irritation of the bowel. Grapes are supposed to be high in natural anti-inflamatory properties. I know that they are very high in salicylates and we avoid them on the Feingold diet. Perhaps there is a correllation. I am assuming the blood is red, not old black tarry. I hate to say it but the cure-all for gut pain is Pepto-Bismaul, on an acute basis only. I had Montezuma's Revenge
in Cancun and thought I would die for the abdominal pain, gas, etc. The Pepto cured it with one or two doses.
Pepto does have some salicylates in it though and that can cause its own issues if taken regularly. But there is something in it that addressed my gas pains. It sounds like the mechanical fiber, or perhaps the pesticides are irritating the bowel, imnsho. Chilean grapes are very, very high in pesticides. So, we do not eat them from December to May when US grapes are unavailable. I'd quit the grapes and see if things improve.
Another consideration is that fish oil does thin the blood (more free bleeding from irritated "wounds") and I don't know the doses that you are taking, or if that has changed recently.
Oh, and you might try some "Gripe Water" which is just fennel and ginger. It is the best natural cure all for gut/stomach issues. Or, try adding feenel and/or ginger to the Green Glop. There are issues if you eat tons of ginger, I believe, but I don't think most people could stomach too much.
You might also try massaging lavender in a clockwise direction onto the abdomen. I don't know if it is the lavender oil topically or the aromatherapy that has a positive effect on abdominal discomfort. I don't know acute homeopathy, but I am a big fan of that route too. It helps one to heal yourself.
I think it is the pesticides.