How to increase milk production?

Hi ladies, yesterday I was desperate, my 3 week old could not sleep properly since 8pm till 12:30am, only 15-20min naps, deep crying and not sucking properly, only few mins and being fussy afterwards. I realized my breasts were not full as usually. Maybe I did not have enough milk, my husband went to buy formula, I sterilized the bottle, we fed her and no more crying. Can u suggest how to increase my milk supply? Until now she was gaining weight properly.