I had dreadful pain with both dd's and unfortunately moved onto formula because the pain was too much.
It was only afterwards that I heard about nipple vasospasm, which i think I may have been affected by. I believe these are the signs (but someone more knowledgable may correct me)
Nipple changing colour (blue, then blanching)
Pain throughout a feed and when expressing
nipple sensitivity at other times (i couldn't even bear the water from the shower hitting them).
Everyone I saw, including bfc couldn't understand why I felt pain throughout the entire feed (like a saw blade across my nipples). I think it was not noticed with dd1, because my latch had been bad and I had awful blisters and cracks, dd1 had thrush (as did I) and she had a tongue tie so kept slipping off. I tried to express feed, but only managed about 6 weeks (it also hurt to express). With dd2 she latched on perfectly straight away, but I still had unbearable pain.
I just thought I'd mention it, because no-one mentioned it with me until it was too late, but I think there are things that can help (I think there is more on Kellymom.com)
Good luck, and I hope you find something that helps.