Neosure

Hi, I'm a mom of a 2 week baby boy, we were in the NICU for bout a week his doctors want him on neosure formula because of his weight and blood sugar, but I cant put my breast milk in with the formula anymore, I have fully dried up, and he cries and screams while he poops, his doctor told me it is normal, until his little body gets used to the formula, I dont know what to do. It makes me cry, when he cries like that, all I have been doing when he does cry and scream, is put his on his side, and help him get rid of his gas. I need some help.