Vibrate and Volume Up

My iphone suddenly stopped acting weird, the volume up button doesn’t work most of the times, by that I mean that, when the vibrate switch h is off and I click the volume up, it acts as the vibrate switch and goes back again, the phone even vibrates when clicked, it’s I can see the silent mode poping up back and forward. Another thing is when I switch the vibrate button to vibrate only, the volume up button doesn’t even react to any click. What could this be and how can I fix it?