Constant blowouts?

MBush4

Two weeks ago we switch our then 3 month old into size 2 diapers. He was fitting in them  weight-wise and we had no problems. But then starting about a week and a half ago it seems whenever he has a poopy diaper it's a blowout coming out through the top and/or legs. What are we doing wrong? What can we do to prevent this from happening?