Okay, I had this same problem with my 3DS, but I know what's going on. There is water inside of your screen and it's messing with the touch sensors that are in the screen. (The touch sensors help feel your tap on the screen). I advise you take it to a repair shop, but if it can't be fixed, try getting a new phone.
I've broken my front camera from dropping my iPhone 5s, even though it DID have an Otter Box on it. Just because you have a case, doesn't mean your camera is FULLY protected. Your camera has a lens inside it that allows it to see. But if the phone is dropped too much, this could damage, shift, or destroy that lens. But thankfully, nothing else will be damaged (if you have an OtterBox case, this is true). Some people don't mind their front camera not working. Be glad that no one will be able to see your face if they hack your phone. -Someone On The Internet