Acidity and vomiting. Feed him formula.

My son is of 45+ days and since birth he has been on breast feed plus formula feed i.e. Nanpro Excellapro 1. From last couple of days he has been spitting up milk or vomiting curdled milk after each and every feed. I have also observed acidity issues. While sleeping he gets irritated because of that reflex and sometimes it feels he has been choking because of that. We do burping for more than 10 mins, feed him on upright position, small frequent feedings but either it is breast milk or formula..he vomits curdled milk every time. We checked the wieght and it was 3.77kg on 45th day and the birth weight was 2.805kg. But it feels very bad when we see him vomit every time. I am not sure if Nanpro is creating problem or anything else. Also we tried feeding him top feed with bowl and spoon but he gets very irrittated with that and so that didnt work. Please note that my breast milk is not sufficient for him for the whole day and so i have to feed him formula.