I need help , my 22 months old baby does not sleep threw the night, she was never a good sleeper since birth,?

she wakes up every 2-3 hours drinks milk and go back to sleep. i am so tired and also i will have another baby in 6 months so i really scared how i will deal with twokids who will be waken up all the time.i also tried not to give her milk at night just water she would wake up crying and would not go back to sleep for hours, i am so exausted