do you pick from the wrist or from the elbow, or both? I play from the elbow, I used to pick from the wrist and sometimes this gave me wrist ache. I heard somewhere that using the elbow alleviated some discomfort because it's a bigger joint (not lots of fiddly little ones). Lots of players do use their wrists though and don't suffer discomfort, I agree with Chris, try and relax a bit!
In summary, what you need's a big joint.