till 6 months of age is the best for your baby.
If you are on a nutritious diet (plenty of fruits, vegetables, nuts, milk, egg etc) and having adequate rest- there is no reason for reduced milk output.
Also please bear in mind that once you start supplementing with formula- your breast milk output will start reducing. And for all reasons, breast milk is the best for your baby.
These problems of colic- gassy, grunting, fussiness etc will be more with formula milk.
Please make it a routine to burp him after each feeds. As a part of routine massage
add these strokes to the tummy- circular strokes around the belly button, strokes in the form of inverted L and inverted U.
when he cries excessively- try to keep a warm towel on his tummy.
You may also ask your Pediatrician
for medications like colicaid- that contain simethicone
and fennel seed oil- which will be of use in gassy infants.
Hope my answer helps you.
Wish your baby good health.