Eating less ??!!

Destiny

My daughter is a 30 week preemie, shes 2 months now so shes almost at what wudve been her due date. For 2 weeks she was eating 2-3 ounces. Now the last week she went back to eating 1.5-2 ounces. She still wakes up every 3 hours to eat but i cant get her to eat more. Is it normal for her to have eaten more for 2 weeks then go back ?