Both of my pinkies are causing me problems. On my left hand its all straight and I cant really change notes that fast in the high register and it sounds sloppy and uneven. ON my right hand, it gets all straight and then causes my ring finger to get straight and then it causes some pain and also makes my fingers a little slower, I need fast fingers for Liebbermann's seconed movement of his sonata op. 23
find some good technique exercises, such as playing a D to Eb over and over, SLOWLY! the repetition can help it to relax, make sure you have no tension in the wrists and shoulders...
the slowly part is key! I'm double-jointed and have had to fight with my pinkies a lot. Go very slow, no matter how ridiculous you feel, getting your fingers and hands used to playing exercises and pieces perfectly relaxed. Then gradually play slightly faster. If at any time you notice tension, even just a little bit, go back to a slower pace & get that perfectly relaxed feeling back. Give yourself time and you'll soon be playing much more relaxed :-)