Oh thats just puberty and the growth spurt. It makes your larynx grow as well...which will make your sound system get a bit deeper, ala the typical "becoming a male" thing when the voice starts to deepen and change. Not much you can do about it. Actually there's absolutely nothing you can do. Your register will change because your setup changes. But that change can end up making you stronger, especially if you were strong to begin with. You could be trying things in the wrong voice/register. You might not be able to hit the same notes and this could be limiiting you with tension if you try to hit the same ones with the same punch. You may have just incorrect techniques now from trying to accomodate for the changes.
Can anyone post a sample? I'm not familiar, right off the bat. But from what I remember its just a real throaty rasp probably in head or lower. Probably not falsetto. Probably blocked off so much that its more like a pressurized grunt, like youre taking a hard dump, with pressure from the diaphragm like crazy. The key is to being able to build up the pressure behind the closed corRAB false corRAB right before you activate them for sound, all the while keeping the throat relaxed. (Though it is best to do them at the same time, which in such a screaming nature would take some time and strength.) I'll hold off anymore comments to I hear a sample. I'm on dialup usually so, just a sample, not a whole song. (unless I ask for it later after liking it alot!)