What position are you feeding him in? With my poor latchers, I found that feeding via football hold helped the latch. I am going to guess that the pain is due to the poor latch. . .if they don't open wide it does hurt. However, just be aware of thrush as a possibility . . .
As far as the extra feedings. . .that's prime time for a good old fashioned growth spurt.

I'm guessing that he's not actively sucking for an hour. . .but just kind of hanging there. It's fine. . .but if it bothers you, then by all means break his suction.
If you are not switching sides at each feeding, have you considered/looked into the possibility that you have too much milk? Based on the amount he's gaining and the fact that you are not having supply issues, it sounds like you have a lot of milk - which can in turn affect supply. There are tricks to fix that if you think that is the issue let me know and I'll tell you how to work with that.