Hi! I had the same problem with my son at that age. He is now 11.5 months.
He would nurse only one side. Sometimes only for 2 minutes on a good feed, sometimes only 2 sucks! Then burst into tears. I would put him on the other breast and the same thing would happen. We would both end up frustrated and near tears almost every feeding! In hindsight, I had a couple things going on. He was constipated from the doctor putting him on solids too early (barley cereal did NOT go well and it tooks us several weeks to get back on track...I dumped all solids and went back to just breastfeeding). So, we fixed that. But we still had the problem. Just not as bad. I don't think it was his teeth, but I could be wrong. I kept checking and there was nothing while all this was going on.
But what I did in the end was pure persistence. I never gave him formula. I only gave him the breast and only at the "right" times to be on EASY. He was fed at the same time EVERY day. I changed two things -- 1) I used to lie down with him, but changed to sitting up; and 2) I bounced him back and forth between breasts, over and over and over. Sometimes for 1/2 hour or so. Just tried as hard as I could. Usually we still ended up both upset. But I just kept doing it and never gave him formula. He was gaining weight like a crazy little man. It eventually worked and here we are, trying to decide when to start weaning!
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In the end, after fixing the constipation, and as strange as it sounds, what I think happened was that he was so hungry he didn't want to "work" for he hindmilk (it gets thicker as they drink, right?). So, I would start on one side, he would drink all the foremilk, I would switch to the second breast and he would drink all the foremilk and then the hindmilk. Then, I would switch him back to the first breast to finish the hindmilk. Does that make sense?
Maybe if he's a big, growing boy he just doesn't want to "wait"? Just a shot in the dark...Not sure if it helps...