I have been dairy soy free for over 2.5 months. back before LO was diagnosed he had awful green/watery/explosive/mucousy poops. they all tested for positive for blood. took 3 weeks off dairy/soy for poops to look better/stop having blood. now the mucous is back but the color isn't green anymore. just brownish/yellow. what else could cause mucous???? if there isn't any dairy or soy in my diet. of note he has been on prilosec and has been drooling a lot more and pooping alot less. he also has had some alimentum formula and I did attend a wedding which may have given me something I shouldnt have eaten. the formula and possible bad food were around 7/9 so would he still be having bad poops all the way from there?                 
                             
        
Re: what else besides MSPI causes mucous in poops?
Not sure what could be causing the mucus in your LO's poops, but I can tell you what my experience was.
M has MSPI, and he had green, bloody, mucus-filled poops almost from the beginning. After cutting out dairy and soy, the blood disappeared and the colour returned to normal, but the mucus was there for another 3 months. We tried eliminating various foods and finally discovered that he cannot tolerate eggs. We have not seen mucus since I cut out eggs several months ago.
Maybe talk to your pedi and see if s/he suggests an elimination diet?
2 things I can think of. First, if you have a foremilk/hindmilk imbalance and he's getting a lot of foremilk, that can cause green, frothy, possibly mucus-y poops. Here are two resources about foremilk/hindmilk imbalance:
https://www.kellymom.com/bf/supply/foremilk-hindmilk.html
https://breastfeeding.hypermart.net/toomuchmilk.html
Second, if he's really drooling a lot (possibly teething?), the drool can affect his output. I don't know if it would be mucus-y, but it can definitely make things runnier and more acidic.
I think I'll try cutting out eggs. how long after you cut out eggs did the mucous go away? TIA!
THANKS! I don't think its an imbalance b/c I don't have an oversupply at all. I constantly worry I don't have enough, and the poops aren't green anymore, just mucous. LO has been drooling a lot more and I did wonder if the drool could make his poop mucousy. maybe that's it?! they both showed up at the same time I think
Sorry for the delay. I think it was about 2 weeks before the mucus was totally gone. But we haven't seen it come back in almost 4 months now.