Refuse to drink milk

Hello mummies, I have been exclusively breastfeeding and my 14months baby usually drinks from the bottle while i'm at work. But for the past few days he's been refusing bottle so suddenly. Even tried giving him breastmilk from him sippy cup, took 1-2 sips and shook his head no. Also tried changing bottles too. So the only time he drinks milk is when i'm home to latch. Does this happen to anyone? Kind of concern that he's not drinking enough milk. Any advice?