Your baby has no reason to have so many episodes of diarrhoea if the hygiene is well maintained. First and foremost look into that and if needed correct anything you may be doing incorrectly. At this age a baby should get boiled cooled water. Ensure that this is so. Do not let her drink bath water. When she has an episode of diarrhoea please check a stool sample for infection. If there is infection there will be many pus cells on routine examination of stool and then there may be a need for an antibiotic. If the stool is not full of pus cells, then just a preparation like Vizylac may be enough, ask your doctor about this. Encourage regular food habits and she will surely gain weight.