What does the teacher have to do with your practice time (how much and quality)? Even if you only practiced the same stuff from that last lesson for the months that the teacher has been gone, you would have been able to improve or at least maintain.
The truth is that YOU have not been respecting the direction that the "amazing" teacher gave you. Bad practice habits now have lead to serious playing problems and a mouthpiece is supposed to help.
Like I told Dennis, I wrote "if you were my student". You are not, so you have plenty of other options. If the only option is to keep the face trashed, then I guess you know what the result will be (although I consider this to be lying to yourself). If I was your trumpet teacher, I would explain to the school teacher in charge what was going on and work something out. They would have plenty to be happy about if you got your face straight. Never met a music teacher that didn't reward initiative and consequence. Met quite a few that "punished" mediocre however.
You need some dedicated building time and you are not going to get it by making excuses. YOU alone are responsible for motivation. You alone are responsible for how you play. You are alone are responsible for the direction that you take. You can crash and burn or wake up and do something about your situation. You can stay in band. If band is graded "every day", I don't know what you expect from an internet forum.
In any case, I know where you will be in 3 months, 6 months or a year from now. Prove me wrong!
p.s. Why can't highschoolers ask for help BEFORE Christmas break when they would have at least some additional time to work out stuff. We generally only get posts like this the beginning of January and September. Forget that I asked. I know why......