It's seem a interesting topic for me because i have the same trouble like you and the same question like you after researching about histamine.
I think i have to do an experiment. I using both anti H1 and anti H2 drug before eat something that i think it can causing the problem to my stomach and it's seem that my stomach is better, no go to toilet after eat or in the morning (at least currently)
. Because i not sure it's can effect for all time and each case in each people are different so i hope my experiment can help you in your case.