Nursing is a relationship. It involves both of you. Your needs deserve consideration too. It's actually a great opportunity to help your little one understand that. It's important to look at your motives carefully and balance them with your child's actual needs. At the same time, you need to be fair and reasonable with yourself. It doesn't help your child grow to see you denying your own reasonable needs. As your child grows older, s/he can handle more limits. Gently placing limits is not contrary to CLW.
I nursed DD through my pregnancy w/ DS. My nipples were sensitive the whole pregnancy. I had to place time limits on nursing b/c it was very difficult for me to bear nursing at all. I explained this to DD (who was around 2.5-3 at the time). I told her I'd give her a count to 10 when my nipples needed a rest. I'd nurse her for as long as I could, then tell her I needed to count to 10. After that, she'd usually pop off w/o a fuss. She nightweaned during my pregancy too b/c I explained I needed a lot of sleep to grow a baby. Later, when I was tandem nursing, it was harder for me to stay patient. I wasn't quite as considerate as I should have been. Still, I did set reasonable limits...always with a gentle explanation. She didn't always like the limits, but I think she grew to understand that I had legitimate needs too. and it gave her the opportunity to be generous.