I swear by huggies, i started my daughter on pampers when she was newborn but i had the same problem you are having & found i was having to change her every hour or so because after that she would start to leek through and would start to go really heavy and horrible.
So i changed to huggies. I have never looked back since, they are much more stronger and hold alot more. Its worth a try- just get a small pack to try.