Transition to Formula...gagging/ throwing up?

Chantelle • Trying for #1 since Oct 2013

Hi there. I have been weaning my son off breastmilk for almost the last month. I have mixed my frozen breastmilk with nestle good start formula. Anytime I've tried to give him a bottle of straight formula he gags and throws up. However he is fine with like 5oz formula with 1oz breastmilk?

Has anyone else experienced this? Any recommendations- should I switch brands?