I agree with others that it sounds like your bub has an issue with the let down. My dd used to be fussier on my left because of it (ouch, I can still remember the pain she caused!). I knew a woman who would pump until the let-down squirting bit had passed and then put bub on, then she also ensured bub got all the hind milk (I think she used to give the pumped milk to her toddler lol).

As others suggested, try lying down, or feeding after the squirting stage has passed and see if that helps...

The only other thing I thought of, is if bub is in fact comfort sucking (which is totally fine) they sometimes get annoyed when milk comes...when all they wated was some sucking. I used to try a dummy, but dd wouldn't take it, so I used to feed through the fussiness and needless to say, dd was ginormous by 3 months. They soon learn how to suck without getting so much milk though.

HTH