Breastfeeding and returning to work

For the moms who went back to work and breastfeed and pumped how did you guys do it? I'm returning to work on Monday, and I'm afraid I won't be able to pump enough. I have some saved in the freezer but I was wondering how much did your baby drink for a full day at the daycare? Also, did you guys pump on your lunch break? My daughter is 4 months if that helps.