Diapers

Ok so we've been using luvs since they are cheaper than pampers (He blows out too bad with huggies), but lately I've noticed a urin smell when he pees. We just upped his size last night and I haven't tried luvs yet with the new size, just pampers and haven't noticed the smell. Has anyone else had the problem with luvs or was it just bc he needed to move up a size? It's strong enough to make me nauseous when I change his diaper which is rare for me.