Mixing formula and breast milk

Rachel

My LO has never nursed, he’s refused since day one so I have been exclusively pumped since day 1. Out of nowhere my supply has dropped and won’t pick back up. I’ve tried everything and nothing has helped. He is eating 3.5ish ounces of breast milk but now my supply can’t keep up. I’m unsure the ratio to do with breastmilk and formula mixed. He’s 7 weeks old this Wednesday and weighs around 10-10.5 pounds if that helps. Can anyone help?