I think the true measure of success as a teacher is not how many students you have in all-state band, or how many competitions your band wins, but whether you 1) genuinely care about your students... 2) are doing the best you know how to teach them, while constantly working to improve... and 3) that they actually LEARN something.
Winning contests is as much a function of the talent of students and available resources as it is the teachers. In other words, don't beat yourself up. You're only part of the equation. But don't blame either. Accept where you're at, where your program is at, and just do the best you can improve a little each day. That's all anyone can expect from themselves, or others.
I would also suggest being more mindful of your thoughts and attitudes. If I'm not ACTIVELY managing this area, it is VERY easy for negative thoughts and emotions to creep in. Life is that way. I recommend an excellent little book called "As A Man Thinketh" by James Allen. It's been out a while (published in 1902) and uses archaic language, but it can be life-changing. The mind needs "feeding" just as the body does.
I hope this is helpful. Best of luck!