My bb also came across this when he's 3.5 months (when I stop breast-feeding him). I feed so bad and this has been lasted until his 6 months old (when I help him to change to a different brand No. 2 formula milk). :-(
During that "tough" 2.5 months, I have tried to feed him 15-30 mins later, when he just took 2-3 oz. Sometimes it works and he may take 2-3 oz, but sometimes not.
Overall, you'll need to be patient, and I'll try to feed him more often...