Baby not taking enough formula feed.

Baby was born pre term in 36th week... her birth weight 1.98 kg... age is 3 months...present weight 4.8kg.... till she was 2 months old she took bottle feed properly.... per feeding she consumed 3 ounce.... but now after turning 3 months old she is refusing to take bottle she is removing it by tongue or else chews on it or else starts crying loudly.... its difficult to feed her by bottle... i have tried so many brands of milk and even changed her bottles nipples and flow ... i dont have enough breast milk supply.... she sleeps while breast feedind and doesnt feed by bottle.... what could be reason for this behaviour?? I tried nan pro1, aptamil, enfamil, nan pro excellence.....nothing worked... her doctor has recommended to start with cerelax when she turns 4 months old...