Iphone 4s sound mutes randomly and won't turn back on?

I've been getting problems with ios7 ever since the update; what happens is when i go on youtube my sound mutes and when i try to turn it up or down, the picture of the ringer comes up with no volume bar, my mute toggler isn't on mute either. But when i go into ringers the sound works perfectly fine with ringers but for some reason can't work in apps, its really been agervating me lately and it usually happens at night or when i use an app for a long time like youtube.

May be software problem.

This happens to my iPod 5th generation it sucks, it's like it goes fine for a few months then all of a sudden it plays up for a few weeks, then it goes fine again, I think mines due to steam from when I take it in the shower though. But yeah I can relate to all of that! I still haven't figured out why or how I can fix it.