I would guess its down to one of two things. It may just be that your foot is too wide for the shell and it requires stretching or punching to give more room for your foot. The other option is that your foot is pronating because you dont have any support in the boot. If your foot pronates your ankle will lean inwards and often this can cause the side of your forefoot to hurt, as your foot works like a lever in the boot. More then likely its a combination of the two.
Probably all you need do is go have the boots fitted. Get some footbeds, get some shell work done and then have a heat mold done.