My Daughter Is 4 Months Old And I Believe She

my daughter is 4 months old and I believe she has reflux. my son had it as well and I was told by his dr to add cereal to his milk to thicken it so the milk will stay down. I have tired this with my daughter and she still throws up quite a bit after every feeding. I have tired increasing the thickness of her milk by adding additional cereal but that doesn't really work and she seems to now be constipated or have hard solid stools. Any advise? T
hank you in advance.