K.P.
M., the same thing happened to my son around 4 months! i thought maybe it had to do with teething or because he started going to a sitter. the first couple of days were very hard emotionally because he just refused the bottle, so while he was with the sitter he didn't eat. we ended up trying just about every other bottle out there and he finally took to dr. brown's. the one he used before that had a big nipple base, and i don't know why he all of a sudden changed his preference, but the smaller nipple base of the dr. brown's seemed to work for him. he's still using it today. best of luck!