Intermittent problems with apple watch

Apple Watch is 18 months old. Recently the hard button (upper right) has become intermittent. I tried to reboot it several times... at first rebooting returned its function, but after a few days of rebooting, the hard button remains malfunctioning. For example, at times it does not allow me to click out of an app page. Additionally, this hard button does not activate the vibration, after exposure to water, when the blue raindrop has been activated. Another recent problem is that Siri frequently starts asking me what I want, without my having commanded her by verbal or hard button command. When this happens, of course, it is impossible to turn her off because the hard button isn't working. Note, the watch functioned very well for 18 months, and this problem has been getting worse the past few days.