Heart breaking change

So, I need some support. I switched my son to formula and it's killing me.  I feel like I failed as a mom for stopping breast feeding.  I've cried so much the last few days. But I only get foremilk which wasn't filling him. So it was so hard he was hungry every 30-60 minutes.  I get a lot when I pump but it isn't filling. I can still give him it with his formula. But I'm just hurting so much.