when i am puching my bag i occasiolly check my form and make sure my wrists are the way they are supposed to be. i don't have bad form because i always make sure its right. i also noticed you said that you said your hand gets cramped-make sure you are not holding your fist to tight or it will cramp. your hands should be free until the moment of impact. and when you mean sore do you mean knuckles sore or hand? on the other hand you might have really weak wrists and like bri bad teeth thai said you should wrap them. but also keep in mind i don't use boxing gloves i use grappling gloves.
but personally i don't think its the bag.