Hi regina, your son's age is around the same as my daughter. 3 weeks old baby
For me, her day starts at 7 am, where I will get her ready for her bath, follows by her feed and some interaction time and the next feed and nap. She normally settles by 7 pm after I wipe her and change her clothes (where her day ends and she knows it's night time). I reckon you have to slowly adjust his timing. You may wish to slowly introduce a routine, letting him know when is his day starting and ending.
Like your case, my daughter's feeds are normally 90ml each time (every 2-3 hours) but recently I realised that she is not fully satisfied so what I did was to give her 100 ml. She can finishes it at times so I suppose it is okay. (Sometimes she takes lesser than 90 ml for other feeds). So long the overall height and weight is appropriate, I feel there shouldn't be much of a problem.