Is It Safe To Give Similac Neosure For A 6 Week Old?

My 6 weeks early premature girl baby now 11 weeks old. Using Ossapan-d, Jesse-D, Trifer, NeoPeptin, Aristrozyme, and Domstal. Breastfeeding and once a day Similac Neosure. Not able to catch up the required weight. Feeds only 20 minutes. Hard to Burp. Because of Gas problems wakes up often. Please suggest any remidies to keep this baby on healthy growth spur.