Why does my iPhone's silent button not work?

Ok soo... A week or so ago my iPhone 6s Plus started (when I turned it to silent, using the button the the top left side of the phone) to constantly switch between silent and not-silent (I don't know what else to call it) and make that vibrate noise like every time it switched so all day I just felt random vibrations. Today I tried turning to silent and found that it would not change. The display did not appear that it was in silent and neither did it vibrate. I can still adjust ringer noise and that works but I can not operate silent on and off. Please help me figure out what's going on. I've had my iPhone for over a year now and I've always caught it when I dropped it.