i started about 6 mts ago, got hand and wrist pain even just on pads, before using the heavy bag. of course it got worse when i used the heavy bag. i was counting on just roughing it out (which you can do, don't get me wrong), but then soemone on this site told me i would end up a featherfisty guy like malignaggi, that was really low blow man whoever told me that, made me so scared, seriously. anyway i went on vacations and didnt train for about two weeks and the apin went away. but now i'm going to strengthen my hands before starting to hit hard again, knuckle pushups and all that, when i use the heavy bag i just do soft repetitive hits to improve the technique. i think this would be the sensible thing to do in your case. im gona start throwing bombs again in a month. alos make sure the impact of your hits land on the right part of your hand, otherwise you can seriously bust stuff, like if your wrists is bent back too much.
a beginner usually experiences this type of wrist pain when they start hitting the bag,the main cause is improper hand wraps installation and improper bag hitting,make sure the hands are wrapped properly,and when you hit the bag dont throw wild haymakers,i think you should wrap your hands and stand in front of a mirror and just throw punches,throw a jab a right step to your right throw a left feint over move to the left duck under jab,then start mixing up the punches,after a couple weeks of solid shadow boxing you should be ready to get the bag in motion:think