Hi Jessica,
Welcome and Congratulations on your pumping and nursing success.
When did you wean from the pump during work? How often does he nurse during the day/work hours on the weekend?
I had this trouble when weaning from the pump with my dd, Olivia. She stopped drinking bottles, but I had to keep pumping for comfort. In the meantime, I had dh give her the EBM in a sippy cup and/or mix it with things so it wouldn't be wasted. I'm not surprised by the Monday effect. It sounds like you are uncomfortable enough that I would pump a little on Mondays. However, just take a little off the top with the pump or hand express...make sure you don't empty your breasts, just relieve the pressure.
It will get better soon, you just don't have any trouble with supply it sounds. Eventually the weekend nursing won't increase your supply on the weekdays so much. Especially once your ds is only nursing for a short amount of time (say, to fall asleep) once/twice during your work hours on the weekends. I had a plentiful supply with both my pumping kids and it worked for me eventually.
Please let us know how you're doing!
Caryn
Nursed Nia for 12 mos, W&P'd for Olivia until 13-14 mos and nursed Afram until 3 years after W&Ping for 16-17 mos.

