There are lots of creams and balms to relieve muscle pain, which I use often when working on a extremely demanding piece. IcyHot is my recommendation.
I have just started out (2nd day!) and was wondering if I should expect small pain (not really pain, more like the hand becoming tense) during the begining due to muscles growing.If I practice for an extended period of time on a demanding (for my skill level) piece usually my hand becomes sore. However, if I let it rest for just ten minutes it feels much better. I've practiced many hours today and my hands have hurt/become sore throughout the day, but I'm about to go to bed and they feel GREAT. I can tell, not only from my improvement in playing, but from the way my hands feel, and an improved speed in typing, that muscles have grown.