if he is gaining weight your fine they drink less milk when it comes to breast milk babys stomachs are small they only need a teaspoon or so. technically we stretch our babies.tummys by giving them two ounces of baby formula i dont think you should worry unless he isnt having wet diapers
even if your boobs feel empty it doesn't mean you're not producing enough milk. your milk gets "let down" during feeding. and most of the milk is actually produced during feeding. so even if your boobs don't feel full, it doesn't mean you're not producing enough milk for your baby :)
what i dod with my other 2 girls i would put a pan on the stove with halfway full of water and then put it on medium let it bubble a little and put the original oatmeal in slowly and then slowly add milk as much as ud like the more watery the better ! for taste i put some honey and a little bit of suger oncase u like it sweet and eat it i love it and it seemed to help alot with my milk production :) i hope this helps and its not confusing lol