Breastfeeding moms - need your help

My baby is both breastfed and bottle fed since the beginning. Now its 50-50. formula and 1 bottle of bf during the day. when im back, i bf her till the morning. I experienced problems with burping for long time and as I said after changing bottles it made a difference. But now that she is 3 1/2 months, she burps as soon as I put her vertical after the breastfeed. So it gets better Uma!