I breastfed DD until almost 2 years. I went in wanting to for all the reasons above, but said I wouldn't beat myself up I couldn't.
The first weeks were hard. I got mastitis, after that I was still in pain, but nipples intact, we were both treated for thrush, it didn't help, I got mastitis again, still in pain after.
Just before six weeks, on the last day 'allowed' I saw a bf advisor. She said she couldn't see why there was a problem, but then said she'd once read something about vascular issues, and asked if I suffered any sort of circulation issues. I always have had cold hands and feet. She said she wasn't an expert but to maybe ask the NCT. I did (they never got back to me) and Google'd like mad.
Turns out you can suffer Raynauds in your nips, I just needed to stay warmer! All the bastard thrush gel had probably made it worse too. A couple of months later I had my first proper Raynauds attack, with the classic white fingers, so self diagnosis confirmed.
Basically, without a throw-away comment and a bigger jumper, I'd have stopped bf at about 8 weeks.