N.,
Congratulations on breastfeeding your son! It's one of the best things you can do for your child! Good luck and stick it through - you will both benefit from your diligence to find an answer for this hiccup.
first, get a second opinion on the tongue-tie.
(I moved this from last) Oh and another thought - he might be thirsty. Try switching him after the first pull-off to your other breast. The first foremilk is thinner than the hindmilk which has the all-important fat in it. It's been warm weather - and he might be looking for a 'drink' as well as being hungry!
He might be getting tired and need a rest - and be taking that rest. if you are comfortable with his nursing you have a good latch - he's getting the nipple where it belongs -on the soft palate rather than the hard palate.
it may be something he just needs to grow out of! a small mouth may be just that - small. He may need to grow into where other infants and babies are on the breastfeeding spectrum.
Best bet - nurse as long as he needs to is what he needs. until he is done. He is hungry of course - but will likely do less attacking when he knows the end of meal/the nursing session is his decision.
Likely he will smooth out his routine in a few weeks to a couple of months. You didn't mention whether he was born early/on time/late.
being paged myself,
good luck,
M.