Thanks for all the advice, everyone. I'm doing everything I can that was mentioned. We've ordered a megaphone, and I'm trying (man it's hard) to raise my voice when I talk. Fluids I've got covered, and apple juice was promptly aquired. I'm working on drinking tea with lemon and honey, but blegh
Pixietricks, I know the basics of the difference between chest and head voice, though I wasn't really shown, so I'm not entirely sure of what's what. I know singing (the higher range) is going to get a resonance in the head, compared to the low notes. The changeover is around D, isn't it?
Hopefully these preventative measures will help. Right now it's not too bad, and if it doesn't get any worse I can be happy with that. Once marching season is over, if nothing else, things will get better.