IPhone has no sound? How to fix?

My IPhone 4s recently lost its sound. I can't play my music or videos without having headphones in. But Siri and my ringtone still work. Sometimes the sound comes back usually after I've had it plugged in charging. I've tried turning it on and of and restarting nothing works. I haven't dropped it or dropped it in water plus it had a big survivor case on it so it should be protected. I recently updated my phone to iOS 7.2 thinking this would fix my soud problems but no. I haven't downloaded any new apps or anything. My phone is barely 8 months old and I've never had any issues with it before. What can I do? I might try taking it to a verizon store if I can't fix it seeing as there are no apple stores where I live.

Try to clean out the speakers on the bottom from any dust or dirt. Also make sure your silent/ vibrate switch is on.