Singers, please help me!?

Whenever I try to hit a high note, I've always been told to breathe from my diaphragm. But now, whenever I inhale into my diaphragm and exhale to hit the high notes, it almost feels as if I'm exhaling too much and my voice cracks. How can I control my air flow so that I can hit the notes without my voice cracking? I've been practicing but now, my vocal cords are tired and I'm afraid I'm damaging them.