Alright
A little background info before you ask:
I have been playing bass for roughly 2 and a half years, I own a MM Bongo 6 (hell yeah

) just to give you an idea.
Heres the deal, I have it so often when I play that my fretting hand and my wrist and sometimes my whole arm cramps up. It just burns like crazy for a while... sometimes I even have to stop playing. Keep in mind I play highly technical stuff, (Dream Theater, some of the crazy Rush songs, Symphony X, etc.

) and I play everyday if I can and for several hours a day if time allows. It is usually only a problem when I'm trying to pull of a crazy fast riff or playing a fast riff repeatedly.
I am just wondering if this is normal and everyone has this? Is this just part of growing/learning? I figured I wouldn't have it this bad if I play so much. I'm thinking it may have something to do with how tight my thumb is pressing against the neck or maybe where I let my thumb rest?
Oh one more thing... My hands/fingers are just kinda average so having a 6 string can be a bit of a stretch on the lowest frets.