LO not drinking breastmilk pumped out from bottle

My LO is 12 weeks and i have tried twice to feed him my pumped out breastmilk but he refuses to have it and just cries. However, when i put him on the breast after he stops crying and drinks. I tried this after giving birth and when i had to stay in hospital and he was fine then but since then he no longer drinks pumped out breast milk. He does also drink formula milk when he has to. Any one else experiencing this?