PPD mainly when pumping?

I do have a little bit of PPD and anxiety at times, but I’ve been finding it hits in a wave almost exclusively when I sit down to pump. My LO was premature at 33weeks and spent 2.5 weeks in the NICU. He doesn’t yet have the skill or strength to primarily breastfeed and requires I use a nipple shield when he does, so I pump and we give it to him through bottle feeding. I pump about 6-9 times a day, so this really starts to wear on me. I will be fine and feel content, and then the moment I sit down to pump... BOOM it hits and I just get anxiety and feel down. Then when I’m done, I feel ok again. Is this weird? Anyone else experience this?