Pumping Problem

I have a Spectra S2. I use a 28 flange on both but since it only came with 1 28 flange-- I was pumping each boob one at a time which was tiring. I eventually used the smaller flange for the right boob to be able to double pump but the suction does not feel the same, I have to bump the suction all the way up to do the job.

A week later, I got my medela pump. It came with 2 27 mm flange so I have been using it since I thought it would be good considering it's a 27 and I use a 28. Well, my left boob hurts a lot while pumping (not the nipple or areola, just the squishy part of my boob). It even hurts until like 5-10 mins after I pump. There is no redness, no warmth, no open areas and no lumps or anything. I am also not engorged. I have very little supply but still want to keep pumping so I can at least give my son what I have.

Could it be the flange size? Any advice or recommendations please? I appreciate it. Thanks