Eh, this is stressful I know! Sudden refusal boleh jadi few things, maybe the bottle teat flow too fast or too slow, or sometimes kena change bottle brand, or ada teething mulai (yes, 3 months pun boleh start). Try a few of us mums, we switch to different teat size or even try nak express and feed pakai cup for a bit, or warm up the milk slightly sebab sometimes they prefer warm. But honestly, since he's hungry tapi refuse, better you check with your paediatrician quickly okay sebab they need to rule out mouth sores, tongue tie issues, or infection, don't wait lah!