Ya it would probably be easier to do week by week until you can't keep track anymore, then go month to month.
I would stick to weeks unail 1 month and then "about a month" "a month and a half" "almost two months" etc...
Not a dumb question at all, I was wondering the same thing earlier cuz I gave birth on 7/7 but not sure if I go by weeks or months but I'd say months just cuz eventually our babies will be like 53 weeks old but we'll lose count by then lol