Apple only supports your device's hardware for the first five years of your its life.
Apple's phone support should be your first contact when encountering problems with your devices, provided you've exhausted community advice on Google and YouTube.
If phone support cannot determine the problem they will set you up with an appointment at your nearest Apple store's Genius Bar. Make sure you've backed up all your docs, photos, movies and music. Make sure you know what items iCloud backs up. For instance, it won't back up movies and songs that you did not buy from iTunes.
Genius Bar employees will run tests on the physical and software components of your device. But if you want to save time at the store I advise that you make sure you have the latest operating system. If that doesn't fix your problem next make sure you have all old or unused apps deleted from your device. If that second step doesn't fix your problem then backup your data then reformat (wipe clean) and reinstall the device's operating system.