I'd suggest getting a blood test for gout (a form of arthritis). It means too much uric acid in the blood collecting in various joints. It usually manifests itself in the toe joint. As a gout sufferer it has usually happened in the left big tow. Recently I had a major attack in my right wrist (didn't effect my playing, but it hurt like hell for no good reason). I had gone for years without any problems when this happened (with an attack on my hip a few weeks later). There's some inexpensive anti-inflammatory medication you can get on prescription which can take care to things when there's an attack. Cherry juice also helps. But, get it checked.