I haven't read the other replies, but just wanted to chime in. I found the recommended holding techniques reall really uncomfortable. My midwife would say "Hold her neck like this, flatten yor nipple with the other hand like that with your hand twisted this way then straighten your back - perfect. Now, relax!" - lol - impossible.
I found it easiest to feed while lying down. In fact, I rarely feed in any other position. That might help you with your pain, too.
If not, go to see your GP. You might have an infection, like tendonitis.
All the best!

Saša