IPod touch question...?

Okay so I have the iPod touch 4g. It's fairly new, not even a year old. I got it at christmas. It only has one tiny crack in the screen. You can only see it if you look really closely. So my problem is that recently when I try to unlock it, it freezes. Only for about 30 seconds and starts to work. Usually when I unplug it does I for 50-60 seconds. Has this happened to you? Should I take it to the apple store? Please help. Thanks in advance!!! :)