The first thing I noticed you mentioning was that you practice as much as you can every day. That can be both good and bad! It's good for the obvious reasons, but bad if you're physically exerting yourself too much. Just like anything athletic, you need to give your body time to recover; otherwise, you'll eventually wear yourself down (rather than building yourself up) and run the risk of injury. So, in that regard, you might want to limit the strenuous practice to every other day; it can work wonders.
Pain is your body's way of saying 'stop! you're doing something wrong!'. Overdoing it is probably the most common problem. It can be a muscle issue, a tendon issue, a neurological problem, or even skeletal/joint related. Stretching exercises are good...but ONLY when they're done AFTER you're thoroughly warmed up. Bad posture is often the reason for pain/injury; there's a reason for 'proper technique'. Stretching exercises can be anything that, well, stretches your hand/fingers...just be sure to start easy, and work up to harder stretches.
As for supplements, after a long period of being unable to play, when I started up again, I was impatient and overzealous, and quickly developed a mild case of tendinitis. I tried a glucosamine/chondroitin supplement, and the problem went away quickly...and has not come back since. I know a lot of people who have used that stuff for a variety of problems, and the results have always been nothing short of amazing. Of course, drinking plenty of water and taking a good multivitamin is always a good idea as well.