iphone automatically lowers headphone volume to mute

For about a week, my iphone 5c keeps automatically lowering the volume of my headphones to mute. I have tried restarting it and reseting the phone's original settings, to no avail. It even keeps happening when I'm not listening to music or in itunes, but the square box that shows up in the middle of the screen will say "headphones mute" with the symbol and it wont come off of my screen until I shut my phone down. So far, nothing has been working. Any ideas would be much appreciated.