Sounds like your having fun, and that's the most important measure. As far as what's giving you problems It's hard to say without seeing you ride. But I'll give it a shot - just based on your description.
I'm not sure what you mean by carve, but I think what your talking about is a high degree of tilt or edge angle. When you ride in bumps or ice it's a good idea to keep a relatively low edge ange or tilt. Sharp edges don't necessarily help because your carving but more likely because they grip the ice better.
In both the circumstances, bumps and ice, you want to keep your centermass over top of your board. You can still tilt the board a little but the more you tilt and lean out over your edges, eg. lean out towards the hill-away from the board, the more difficult it is to balance.
When boarders first discover carving and exploring edging the tendency is too lean out towards the snow-even to touch it. It's fun and feels cool being so close to the snow. But unless you are on a forgiving surface, eg powder, it's difficult to keep your balance. I bet this is why your having trouble changing edges while carving. If your leaning out way over your toes you have to move a considerable distance before you are above or leaning beyond your heels. But that's just a guess - a lot of things could be going on that would cause difficulty.
It's still possible to tilt your board, achieve a high edge angles and use your edges while staying balanced. When your on edge try to make sure your centermass is above your feet and pushing down directly through your edge towards the snow. If your broken at the waist or leaning out towards the hill this is and indicator that you need to bring your centermass back overtop of your feet and direct your mass directly down towards the edge you are engaging.
But none the less a relatively flat board is definetly going to be easier to ride in the bumps and ice. Use twist and pressure more than tilt in these circumstances. This is particularly important when riding on boiler plate, ice. Unless your an olympic snowbaorder or a serious racer you really don't want to carve turns on ice because your simply going to pick up speed and hall ass. Instead try to skid or scarve, a combination of skidding and carving, to maneuvor on ice. Use as little tilt as possible. It is also extremely important to skid at the top of the turn on ice, using your back foot. Don't dump all your speed at the bottom of the turn or your going to chadder or have to use a high edge angle at the bottom of the turn(most likely causing you to loose balance or break rhythm). It's like driving on ice. You don't speed through a turn and break at the end. You break slowly as you enter the turn and steer throughout.
One reason powder is so easy to ride is that it doesn't hurt when you fall. But another reason is whenever you ride deep powder no matter how much you tilt the board, for the most part, it is flat on the surface of the snow. You are creating a flat surface as you ride through the powder. Next time you ride deep powder, stop and admire your tracks. You should be able to see a flat baord track even when you are tilting. That's why we can get away with leaning out and putting our entire bodies down on the snow when halling ass in deep powder. My favorite turns - steep terrain, 25 yard radius, knee deep powder, 40 miles per hour, laying on the snow, 15 foot rooster tail, primal scream toe-side turns. I've only pulled one off on the east coast. 2 years ago on the 41 inch day on off the wall.