I think I hold the pick the same way... but my index finger is definitely a little bent. Also, you should be using a bit of wrist and elbow to pick... nothing should be locked up.

Are you relaxed when playing, or is there tension? Without knowing more, but assuming you're the same as everyone else I've seen with similar problems, you might consider slowing down a bit and concentrating on technique rather than just pushing yourself harder and harder.

Tendonitis is a bitch...