There's a couple factors that could be causing the pain.
1. Your feet might not be in super good snowboarding shape, if you don't ride very much you will probably notice pain alott more then if you snowboard pretty regularly.
2. Your boots just don't fit you right. This is kind of what sounds like the problem, especially since it's cutting off circulation. With a boot that fits right, you should be able to wear them pretty tight, you want them tight since it obviously gives you alott more control over the board. If your current boots are really bugging you, I would advise grabbing a new pair. Try on alott of different pairs until you find one that fits you right, brand/price doesn't really matter that much with boots as long as they are comfortable.
PowderHound and TreeNinja