sounds like you have done exactly the right thing with the breastfeeding

Yep like CL both of my DD's developed lactose intolerance after gastro and we reduced their dairy intake and the loose motions reduced. *** TMI warning *** lactose intollerance shows up as 'frothy' poos, so it kind of looks like gastro but it has less liquid in it IYKWIM

we only have lactose free milk in the house now and the girls (and us) are much healthier for it. Normally cheese and yogurt can be reintroduced after a few weeks with no issues. Good luck !