I have gone through this a few times with my 11-month-old! I (literally) feel your pain. First, I don't think you can do much about crying out in pain when bitten - that's just an involuntary (and completely understandable) reaction. What you can do is focus more on your reaction afterwards - don't get mad or anything, just say something like "I see that you don't want to nurse right now", unlatch, and wait a little while before trying to nurse again. He will start to understand that biting = not nursing, and will over time stop biting if he really wants to nurse.
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Another thing that I did was keep my pinky finger near the corner of his mouth while he nursed so that I could unlatch him the second he seemed like he was about to bite. I did this mostly for self-preservation - it was painful nursing on nipples that have been bitten! - but over time the presence of my finger there was also a reminder for him to not bite. (I don't have to leave my finger there everytime we nurse - I just did it when we were having the biting issues.)
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We have gone through this twice, and using these measures pretty much took care of the problem within a few days. I would also suggest that your check out www.kellymom.com for some other good tips - there are lots of different reasons why babies bite, and they have different solutions.
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Hope you get through this quickly!