don't worry too much la. my bb was like that 2 month ago. after consulting my doctor, i've changed the milk powder. he gradually picked up again. now he can finish 5-7 ozs, twice a day, still a little bit lower (the doctor said the minimum milk per day at this age is 15ozs.) but it's ok la.
try other ways, such as change the feeding time, don't feed him anything (even water) 1 hours before milk.
still don't worry too much. different bb has different appatite, not all bb like milk. especially when he start to have congee and 糊仔.
btw, my bb is now 1 year old.