Ok ladies...for days and days now my daughter has really nasty smelling poops that is like sandy and…

Ok ladies...for days and days now my daughter has really nasty smelling poops that is like sandy and grainy! When I wipe I cant for the life of me get all the "sand" looking bits off her! She hasntt eaten anything different in the past few months. Shes on sensitive lactose formula and has been since she was 2 months old. I have no idea what it could be any moms experience this?