Does this sound like my babies diapers are to small?

My son is 5 weeks old. He was born at 9 pounds 7 ounces so he's pretty much always been in size 1 diapers. Lately my son has been having quite a few leaks out his diaper. It's so strange it'll be like he pees all over the place, but yet his diaper is pretty dry. It comes out the back it seems. As far as poop it seems to be staying in there pretty good. Could we not be adjusting the diaper right and that's why it's leaking? We tried a 2 today and it seemed pretty big, but not horribly big. We just have all these size 1 diapers yet that have to be used because it's all open now. Also where should a diaper be hitting? Like should the belly button be covered? Or should it hit right bellow it? Thanks!