Switching between formula and breastmilk?

My little guy has been having some tummy troubles to the point of projectile vomiting after feedings and screaming in pain from gas. It breaks my heart and there's only so much I can do. I cut out so many foods already and it hasn't helped. So I have some formula left over from when I supplemented his first week before my milk came in that he took pretty well. Also, my supply dropped drastically and I can hardly keep up with him. Would it be okay on his tummy to try the formula for a day until I get my supply back up?