Sorry Soc - i spoke to the trainer at the gym about it, he thinks its a pulled muscle, its not painful enough to have torn a ligament apparently... :-)
i think i need to listen and rest, i keep going back to the gym......
Sounds like a Rotator Cuff injury. I've recently suffered with this and the treatment advised was analgesia, light exercise ( to keep the joint mobile) and heat. I sympathise with you it took nearly 6 weeks for mine to resolve itself.
Another point is; if you use a computer a lot, the position of your arm when using the mouse and the repetitive movement when using the mouse (RSI), can exacerbate the symptoms.