volume problem with Motorola

My phone has started to set itself at full volume all the time. If I try to adjust it it simply goes straight back to full. This has been happening for 2 days now. I haven't dropped it or done anything that might have caused it to glitch. The button on the side to lock the screen has been temperamental, sometimes it works, sometimes not. If I turn off the phone or reset it the volume might work for an hour but always goes back to full. It is driving me crazy. Especially when I want to watch something or listen to something at night, just drifting off when the volume shoots back up to full.