When will my supply adjust?

ILMomma

I EBF my almost 4 month old. I pump three times at work for 20 min each and usually get 2 oz from each breast at each pumping session. This worked for us because my son only eats 3.5 oz. Well my mom who babysits just told me that he now takes 4 or 4.5 oz in one feeding. My question is how long will it take for my body to start making more milk to cover the extra oz i need?

FWIW he only feeds from one breast so i know i have enough of a supply for him when nursing. I just cant get it all when pumping.

TIA