Re: hand cramps
Guitarist Nutritional Centers. Awesome idea. Soon as I hit the lottery....
As for treatment, first go see a medical professional so they can tell you exactly what it is. See several who specialize in different fields: muscles, joints, and even bones, as they will all probably have a different opinion based on the information you provide them, the depth of their knowledge in their given field of study/specialization, and how much money they get from whatever pharmaceutical company products they will write you a prescription for.
Always get a second opinion before committing to a treatment, because even the person who graduated medical school with the lowest passing grade is called "Doctor".
Seriously. It could be a pinched nerve, it could be muscle damage, it could be a weak joint, or it could be a foreign body like a splinter or fine sliver of glass, metal, or anything stuck under your thumb that is pushed into a nerve when you apply constant pressure from holding a pick.
It could be poor circulation in your hand due to a pinched nerve in your shoulder. Or it could be that you simply need to tweak the way you hold the pick, or that the pick is too thick, which requires more pressure to hold, or too thin which requires more pressure to keep rigid enough to achieve the speed and note character you're going for.
Maybe you just need a big variety box of picks to sort through until you find "the one".
Maybe you're pinching a nerve or otherwise cutting off the circulation right at the joint in the middle of your thumb by squeezing too hard?
Maybe your thumbnail is cutting off the circulation because of how far toward the tip of your thumb you hold the pick?
Maybe it's just a muscle cramp from exertion. Do you get them in your calves at times? Have you tried any "home remedies" like eating a banana or drinking pickle juice when it happens? I get cramps in my feet and it feels like my toes are trying to tear themselves free. I eat a few regular dill pickle slices (like what you'd find on a burger) and they go away.