Help me!!!

Since i went back to school and started pumping i've had trouble pumping enough milk, so my daughter would have one bottle of formula at daycare and breastmilk for the rest. this week i finally caught up to how much she's eating (4 oz every 3 hours) and now she's wanting 5-6 oz every 4 hours! This feels hopeless... what can i do to catch up? she is 3.5 months old.