Re: Sore knuckles
If you're sure that's the problem, then try to only tense your fist at the last second before impact. So when your guard is up and you're not punching your hands are open and relaxed inside your gloves and then you only make a full first right before you hit the bag/pads/person.
It should take some stress off your knuckles, it'll add some snap to your punches and you will save some energy.
You may also have your handwraps done up too tight.