Yesterday I had a real blast as I had the opportunity to practice my violin for at least four hours off and on including my lesson. While I enjoyed the nothin' but violin, I noticed that at least fifteen minutes after the last session of the day, my the inside of my left wrist hurt dully. If I hold it absolutely straight, I can alleviate all of the pain and even have a certain range of motion, but I can't bend my wrist back, or rotate it, and God forbid I try to pull my violin out and do vibrato.

I vaguely recall having this problem a while ago. I think that it went away after a day or two, but that feels like FOREVER. It feels almost like the tendons in my wrist are swollen, but there's no visible swelling from the outside or even redness. 

I almost expect carpal tunnel syndrome, except that I'm kinda young (hardly even a teen) and I wouldn't expect to get something like that yet. Also, it doesn't really match the symptoms of carpal tunnel syndrome because if I let my hands hang like suggested for checking yourself, it doesn't cause numbness in my fingers. 

What is physically causing this weird pain, and how can I alleviate it? Is there a way I can avoid it in the future? Is a factor of my playing technique causing it (maybe I'm clenching?)?

Quick edit: I had previously described the pain as "dull," but on second thought I'd call it semi-sharp. It's not like a knife, but it's certainly not muscular pain.