diapers

OK ladies I'm really having trouble here. I have an almost 5 months old and she weighs about 15 pounds maybe less. I have her currently in Pampers size 3 diapers we just moved from size 2 into threes this week. Since I've moved we have had a blowout every time she poops.I have no idea what to do at this point do I need to get bigger diapers? Or do I need to get different diapers?. She has a really big butt and the pampers that I have right now are pampers baby dry . Any kind of help is appreciated. I didn't have this problem with my other daughter