Mommies my daughters been having really bad poops for the last 4 days and has lost 3 1/2 lbs since…

Mommies my daughters been having really bad poops for the last 4 days and has lost 3 1/2 lbs since then is there anything i can do to help her or just bring her into the doctors tomorrow morning? She almost 13 lbs and 15 months old.