you still have to continue the pumping session every 3 hours. if possible, work out thrgout the the 24-clock, best to do a early morning pump or a late night pump before you sleep. if you can, dont miss night pumps and build up the supply from there again.
working mother normally encounter dip in supply but unless you really are strict in yr pumping schedule, else it will continue to dip.
another problem with dipping supply might be ovulating/menstrating for some woman like me. or it is time to inspect yr pumping accessory and check if there is any wear and tear which can cause ineffective pump.