Help!!

So my daughter is 23 months. She is going through a week of diarrhea none stop. I don't know why. She had this on and off her whole life. Everytime we take her in they tell us to stop milk and it milk in tolerant. We have tried that and it does nothing for her, or they tell us it's a stomach bug it will pass. We been going through this on and off sense she was almost 6 months. Either we have extremely runny or rock hard. Rarely normal. She doesn't want to eat with week. When she does very little. Extreme runny poop everyday. I just don't know what to do