I don't know if the blood it is a sign of allergy for sure. What I know is that dd cannot have soy. If I have soy in my diet, then there is going to be blood in her stool as well as acid reflux.
DD had green mucousy and sour smelling stool for a long time. I thought it was my oversupply of bm and tried all sorts of ways (eg. eating bunches of parsley) to lower my supply. Nothing helped with my oversupply until I got dairy out of my diet. I also eliminated a bunch of other foods at the same time and noticed an improvement in dd shortly after.
It's been a while since I've reintroduced dairy into my diet as it does not seem to impact her as much as it used to. The curious part is that my milk supply increases whenever I have hard cheeses.