Not a Doc disclaimer!
Lots and i mean copious amounts of pre-stretch routine and some stretching during the gig/practice day(s). maybe some massage too.
I am on lunch break so this wont be a long post.. but when I get off I will dig through the forum for Fergie Fulton's posts on the subject and drop you some links.
Carol Kaye also has some good dap on the subject. Adam Neely may have some useful input too.
It sounds like you are gripping much too hard on the pick, so you may benefit from a larger plectrum, so you arent pinching as much, or possibly you may need to adjust the grip on the plectrum itself.
when I use a pick I like the big 1.0MM Dunlop kind. and I do not use the tip of my index finger to pinch, rather I rest it between the first two joints... kind of hard to describe: but I put the tip of my index finger on the top of my palm (then relax of course) and I only play with the very tip of the plec.. sort of looks like when Bill Clinton was giving a speech and lays his thumb over his folded fingers... I want to say I adopted this form from Rex (Brown) when he was playing with Pantera.
I may have to find/post a video.. again lunch time is almost over so it will be later this wknd.
but at any rate, some stretching should do wonders and maybe some massage of the area..If it does not, then your problem may be rooted deeper than I can unprofessionally diagnose over the internet on a bass forum

I type a lot for my job so I have a tendency to stretch out during the day as it is...