my BB also. from 160ml drop to 120ml every 4 hours.BB on diet, lost his tummy and double chin.
Then I try 少食多餐 will feed him 120ml (straight on without break) every 3 hours, even in mid-night.
After a few days he is returning to his 160 ml slowly.
My BB is 3.5 months, will not give him 開奶茶 before 4 months. Do not want to upset his digestive system.