Hi L.,
I had major difficulties breastfeeding my first son and while my second one latched on like a champ, he started doing the same thing as your son. What happened with me but I just didn't want to hear (in my case - may not be you) is that I wasn't positioning him comfortably. For some reason, I couldn't tell, but everyone else around me could - my mom, husband, lactation consultant. Once I retrained myself how to hold him, he seemed to do better. My 3rd child started doing that around 6 months and no amount of repositioning, extra pumping seemed to work, so we were done at about 7.5 months. But because I work and had two other kids to take care of, I decided not to beat myself up over it.
And I think many of us who have had breastfeeding problems have experienced very similar scenarios with the people that we talked to. Hang in there, and above all, take a deep breath, try the positioning thing, or any other advice you might get (more than once), and R-E-L-A-X. Much easier said than done, I know for sure. But I also know that the more I stressed, the less milk I produced.
I also tried squeezing my breast as he nursed. It seemed to work for me.
I hope this helps!