Baby feeding time

I'm starting to get worried on my baby's feeding. She's going to be a month old in 3 days time. Started to feed baby 90mils of formula milk. At times i would mix bm with formula. She's been drinking half way through, have to force her to drink up the milk as per dr advise due to her weight from 1.8 dropped to 1715kg. As much as i want her to finish her milk, I can't help it. She's been rejecting milk after probaby around 50mils of intake while feeding. She's bottle fed since birth as she's been warded in High D ward for 2 weeks after birth. So after her 50mils intake, she doesn't want anymore of her milk, instead she kept on drinking abit, cried out loud and push the bottle out of her mouth. Any mommy experiencing the same issue?