I am right handed and had a similar problem: basically over-use was causing the tendons in my right hand to become very uncomfortable. I didn't see a doctor/physio, I just swapped my mouse to my left hand.
It took a two or three days of fumbling around to operate a mouse with my left hand reasonably well. After a couple of weeks it was completely second nature....
Continuing to fence with my right hand, but use the mouse with my left had has removed the problems with my tendons in my right hand. If I do ever have any problems, I know if it is fencing or computer use: fencing doesn't interfer with work and (more importantly

) work doesn't interfer with fencing...
Good luck with it all - I hope that your arm gets much better very soon
Boo