Baby rejects milk

My baby is 6mths and since 4mths, he doesn’t want to drink milk. If we try to force him, he will vomit all out. So we reduced his milk to 100ml every 2-2.5hrs. But still, he always cannot finish and need to warm the ebm again to feed later. We even resort to using syringe sometimes in order for him to drink around 700ml daily. His percentile dropped to below 25% and we were referred to KKH, where the doctor gave useless advise such as increasing his milk vol to 125, and must meet 1L of milk each day. I tried changing milk bottle but it didnt work and PD said he doesn’t have oral thrush. Anyone has any advise how to make baby drink more milk?