like it was mentioned, just stop using a mouse. The first time I did a serious modeling assignment which lasted me about 4 weeks, the same thing happened to me. Luckily I stopped right away so it never got very serious. Wear a brace, take a break, get some sleep, and if you must finish the assignment, switch to a tablet. It's lots healthier for your wrist, and you can set your tablet pen button for middle click.

I never use a mouse anymore, not even @ work. And so far I've never had wrist problems again =)

Take care of yourself! And if you need any help with 3D, feel free to contact meee~