My DS2 had/has a very strong suck. It still hurts sometimes now, at 10 months! He had sucking blisters on both lips, all the way around (not just the little tiny one you often see on the bottom lip), for months!
Thankfully, I have a high pain threshold, and am very determined. And even so, it really really hurt at first. One good thing, though, he never fed for very long at all. And my supply was always good.