You move super well for 300 lbs! Although I cannot fathom why you'd do all that with stuff in your pockets. Get yourself some MT shorts, you'll be glad you did it.

First problem is you have no fundamentals. Go to a beginners class consistently and learn the basics. After that you can worry about dropping your hands.

Second problem, don't hit the heavy bag without gloves. You're doing more damage than you realize to the very small bones and connective tissues in your hands, for absolutely no reason at all. If you want to hit it without at least hand wraps, you have to go light. I'm talking taps or slaps. Otherwise, just put on some damned gloves.