Pain in that area at your age is most commonly due to tenosynovitis, that is, inflammation of the covering over the thumb tendons, either due to direct injury or due to overuse for some specific activity or occupation. It takes a few weeks to resolve completely. The more rest it gets during this period, the better the healing and lesser the chances of relapse. If it does not subside by 3-4 weeks or recurs frequently, you might benefit from a local steroid injection around the tendon.