If you have not yet done so, it may help to update your iPhone and Apple Watch to the latest software versions (presently iOS 9.2 and watchOS 2.1). Instructions for updating the software are available here:
- Update the iOS software on your iPhone, iPad, or iPod touch - Apple Support
- Update the software on your Apple Watch - Apple Support
Unpairing and re-pairing your watch may also help to resolve any software-related issue.
Otherwise, if you would prefer to have your watch checked under warranty, contact Apple Support (mail-in service may be available) or make a Genius Bar reservation: