IPhone 4S front camera problems?

I bought an iPhone 4S around Thanksgiving. And about a week or two after wards I started having issues with the front camera. It gets dark, and blurry, and looks like is is glitching. I took it into an apple store and they reset it and said the problem was resolved. But it started happening again a few days later.
if you are wondering, I'm very careful with the phone, I have an otterbox on it, and I have only dropped it once, but the problem was occurring before I dropped it. What is the problem?

Try restarting the phone. If it still doesn't help, take it back to the Apple store and tell them that you brought it in once and they did something to it and they said they fixed it, but the problem is still there. They will probably give you a replacement then.