Aww I understand lah, that refusal phase can be so stressful especially when you're trying to juggle BF and FM! A few of us went through the same thing around that age, our babies would suddenly reject the bottle or throw up after a feed, and honestly it's usually because they're either not hungry enough yet or the flow is too fast for them. Since your milk supply is lower, maybe try spacing out the FM a bit more and let baby get properly hungry in between, or check if the teat size on the bottle is causing him to gag and vomit. Best to mention this to your paediatrician though, just to rule out any reflux or feeding issues, since vomiting combined with refusing feeds needs a quick check-up to be safe!