Whats wrong with my iPod?

I just got a new 4th Gen. iPod touch this past Christmas. I put some apps on it (about 45). It has worked great for me but recently I've been having some problems with it. I have noticed that several of the apps (especially the ones that require a little more juice to work) have been crashing. I have noticed that the apps Skype and Modern Combat 2: Black Pegasus crash alot. This is kind of pissing me off and I'd like to know how to fix it. Thanks!