*sorry I meant to put this in Pumping not Breastfeeding

I just started pumping to help with my supply since we're supplementing but feel like my boobs do not cooperate with the pump. My boobs are very squishy and are always billowing out around the flange. This makes it hard to get my nipple into the tunnel properly. I started with 27mm shields and they were way too big. I ordered 24 and 21mm ones to try and have had better luck with the 24's but am still waiting on the 21mm ones to arrive.

My main thing is that I'll get good flow for like 3 min then it will barely drip or completely stop. I basically spend the next 15 min moving my boob around, rotating the flange, compression etc. Sometimes this works and I'll get another minute or 2 of decent flow/spray. So far the most I've gotten at one sitting was a little over an ounce. I've only practiced doing 1 side at a time so far until I feel more comfortable with it.

Side note - LO is 3 weeks old and is a super lazy/sleepy BFer and is usually still hungry after a 40 min session - so I'm not confident that he's getting that much from me. I originally wanted to EBF but after a rocky start with jaundice/weight issues and several Mommy meltdowns I've come to terms with "something is better than nothing" and we are both much happier.

My questions are:
1. Does anyone else have to adjust the pump/flanges for flow?
2. How much were you able to pump when you first started and how long did it take?
3. Do you think I should increase how often I'm pumping instead of our long, possibly unproductive BFing sessions?

Any advice/input is much appreciated!