Mommies advice: feeding baby

lo
I'm a ftm & I always listen to doctors because I feel like they are right since they have the degree. My baby is 5 months now, born at 27 weeks. The doctor is saying keep her on 4 ounces of milk since she's premature. But she ALWAYS want more! My mom is saying she need something in her formula now but they're saying no. My baby is hungry every hour to 2 hours. Idk what to do. I'm running out of milk way faster than I can afford & literally get no sleep anymore. Please help me out moms!