Originally Posted by: ffaiellaYou need to play more often for a shorter time likened to working with wieghts. Also, pick a light string guitar, a sweet 12 fret or a grand concert requiring no effort at all, and at last, let it rest or it will never heal. Build up slowly Pal

I agree, accept that you've got a nylon string guitar, so I don't think string thickness is going to be an issue. It sounds like its technique... not your body position... are you really tensing up your arm when you pick? Your arm should be relaxed as you play... a good way to check is to see if your wrist feels really tight as you pick, or if it feels relaxed and floppy. But yeah, take it slow, don't "push through" and if it hurts, stop until it feels better.