My lock button is stuck

My iphone 4s was working fine, then all of a sudden the lock button stopped working. I didn't drop it or anything, it just randomly stopped. I can't turn off my phone, or lock it. Everything else is working perfectly fine. I got the phone 1 year ago. I'm super careful with it, it's always in an otter box and I don't even think I've dropped it anymore than twice since I bought the phone. Please help?