Baby 1 year

My girl 1 year 26 days and till now she had difficulty in passing motion. Every times she will cry to pass motion. She is eating well, fruits, vege.. But water not much.. Difficult to make her drink water too. Brought to Dr, check nothing wrong in her tummy. End up gave her lactulose..but how long will be depending on that right.. Mummy please help me.. I have already change milk to similac total comfort