Frustration at the nipple

I plan on talking to a lactation specialist but wanted to see if anyone else has experienced this. Not sure if it’s a latch issue or an inbalance, but the last couple days when my son latches, he will get about 7-10 minutes of constant swallows, but after that it’s like he’s fighting for milk. When he comes off I can express easily, but he gets frustrated if he doesn’t get a gulp after like 5 or more sucks. I’ve tried changing feeding positions and making sure he latches properly (at least it feels and looks proper). Anyone experience this?? Any recommendations? Thank you!