Take a breath of air. A nice long breath. Now take a breath and hum on the exhale, feeling your vocal cords vibrate and resist the air leaving you. This mysterious process of engaging your vocal cords is the secret to effortlessly controlling your singing voice. Most singers who run out of breath do not actively engage their vocal cords, and their air escapes without the proper resistance from the vocal cords.
My hope for you is that you will focus on your breath for a while as you sing. See how little you can use. The pathway to a breakthrough with your singing is a journey towards less and less air moving across your vocal cords. Your ability to effectively engage your vocal cords and hold air back will allow you to do great things with your singing!