Hey guys, I know you've probably heard people whining on about this a thousand times before, but I'm a beginner on the bass and I'm finding that after playing for over 30 minutes at a time I'm getting serious cramps in my thumb. My other fingers are strengthening up ok, and I'm not experiencing much pain there. But I can't seem to get to a stage where I can get rid of the pain in my thumb. I'm self taught as there are no double bassists in my area, so it's very possible I'm doing something wrong technique-wise. Should I just try concentrate on using less pressure while playing? or could it be something else?? Any feedback would be greatly appreciated. Thanks!