worried about baby getting dehydrated!

Alana • Married | TTC #3 w/ APS | Mommy to 1 girl 👧🏼 & 1 boy 👦🏼 & 3 angels 👼🏼 |
Hi my LO is 16 weeks old and has been throwing up and kind of phlegmy sounding. She isn't acting hungry and is sleeping a lot and barely produced a pee diaper over night which is usually so full it leaks. I'm really worried. The pediatrician said she could have pedialyte but I'm not sure how much. How much do you give your 4 month old?