Trouble breastfeeding

So my daughter is 15 weeks old. In the beginning I was ebf. Well she was born prematurely and was losing alot of weight. Doctors wanted me to pump and give her a little formula well and give her a bottle to keep track of how much she is eating. Well ever since then I've been having trouble getting her back on the breast. She latches on but falls asleep quick. When I give her the bottle she is fine. I have been pumping so much and giving her a bottle afterwards cuz I wanna make sure she is getting enough. I don't no what to do I just want her to eat from the breast but it's like she is lazy now. Any suggestions please