The work days are affecting your supply. The only way to keep up supply is to continue putting out the demand. What I mean is to find other times of day to nurse or pump more often. Pumping is NOT the same as nursing your baby. I don't have a medical explanation, only experience. Nursing more often will help, even if it's through the night at this point. (You wouldn't want to continue nursing through the night long-term due to tooth decay.)
It's amazing that you have a frozen supply---KUDOS to you! (When my second child started sleeping through the night better and skipped nursing, I got up to pump so that my supply would remain the same.) Also, drinking more fluids, especially water, and avoiding caffeine (which you probably avoid already) because it dehydrates you. Document how often you drink and how many ounces for a few days; most people do not drink enough; nursing mothers must stay hydrated. Having a personal water bottle can help gauge your intake. Finally, a good health food store will have supplements you can take to help your milk supply; I have no experience with them so I can't vouch for them. However, if I were desperate I would try the herbal supplements. I hope this helps. God bless!