This could have been caused by overall fluid retention and could be a sign of a serious infection or inflammation. It is important to talk to medical personnel for help. Get more information about these signs on http://www.localhealth.com/article/swollen-finger.
All of those symptoms indicate a possible infection. I'd take an OTC pain reliever and wait until the infection reveals itself. If it gets worse or you notice red lines starting from where it's sensitive, it'd be a good idea to see your doctor.
Sounds like you may have bumped it without knowing or have a under-lining hang nail or ingrown nail. Ice it down and take some motrin. If it gets worse(ie; pain, swelling, discoloration) go to your local urgent care or ER.