Needs more mommas advice!

Hi everyone! So my 3 1/2 month old will refuse the bottle everytime I leave! (I EBF) when I go to work and school, she will absolutely not eat at all, no milk gets in her little tummy for about 6 hours straight until I get home (she's protesting lol) anyways I have called her pediatrician and she reccomended introducing baby cereal at this age since she won't take the bottle. Has anyone given their little ones food so young? Should I get a second opinion?