Samsung Galaxy S3 frequently stuck on lock screen...

[AC Question]

So my Galaxy S3 recently has been giving me some trouble. Every so often the lock screen will get stuck, where touch is completely unresponsive, and I can't get it to do anything. I also have noticed that during this time my phone has been switching from Wi-Fi to 3G to 1X connection (via my carrier, Straight Talk). Once the it goes through several cycles of this it eventually works. My phone has only started doing this about two days ago, and has never done anything like this before. I've tried restarting it, and even a hard shut off (usually I can only get this to work during these condition by removing the battery). I've also noticed that when I turn on airplane mode, the phone works fine until I turn it off. Please help me.