mommies! I need advice and help :( my 6 month old is only drinking 3 oz of formula per feeding every…

mommies! I need advice and help :( my 6 month old is only drinking 3 oz of formula per feeding every three hours. doctor is worried cuz she not drinking enough. we have days where she refuses formula and will only eat solids... won't drink juice or water. how can I get her to drink more formula. pls any advice is appreciated.