I am trying to figure out how in the world to pump between feedings and I just don't know what to do.

My LO is 5 weeks old, and is on a very strict 2-3 hour feeding schedule due to a disorder he has. Usually during the day we can go two and a half to three hours between and at night we stay at three hours. How do I pump in between that without feeling like I'm taking it away from him?

I just fed him at 12 for about 15 on each side, then tried to pump right after for about 20 minutes and didn't even get half an ounce.

Do I have the right idea and my body just needs to get used to it? I really appreciate any help or advice you all have! Feeling kind of desperate and discouraged