What Causes Recurrent Diarrhea In A Child?

Hi Dr, My kid is 1 1/2 year old and a fuzzy eater. Stopped breatfeeding by her 6th month as i am not getting milk even after treatment. She often suffers from diarrhea. Since she dont eat much in day time, i had to feed her (cow) milk in night whenever she cries. She sleeps immediately even before she drinks 50ml of milk. So i use to keep that milk for few hours, so when she cries again, i will feed her the same. Usually in daytime i will not keep the bottle milk for more than an hour. But its difficult in night time. So i may keep till 2 hrs and feed the same. Is that the reason why she gets diarrhea often?