Why is my iPhone volume always muting?

I have an iPhone 6, I realized that my volume was always muted so I tried turning it up and I watched as the volume came up on screen and muted itself once again. I tried on many videos and it mutes itself and doesn’t allowed me to turn the volume up at all, this has caused the volume with the mute sign to always be in the center of my screen and it doesn’t go away so I can barley use my phone anymore ( if it means anything I updated my phone to the iOS 11.0) pleases help!!