4 month old dropping in percentile range

Maegan

My little girl was 8lb 10oz when she was born. She had to be in the NICU for a couple days because she swallowed fluid on the way out. She’s exclusively breastfed; she refuses to take a bottle. She lost a little over a pound while in the hospital. Now that you have a little background, she’s steadily dropping in percentile. She started in the 43rd percentile and has dropped 10-15 every time we go to the doctor. At her four month visit she had dropped to the 16th percentile. Her doctor is concerned, for obvious reason, and suggested following up her feedings with formula. As I stated above, she refuses to take a bottle. I guess what I’m trying to ask is, has this happened to anyone else? I am open to any advice to help her gain weight. I never had this issue with my two older girls; they were always in the 90th+ percentile.