Iphone 5 volume down not working?

So i had my iphone 5 for 4 months already and when i woke up to go to school i usually crank up my music to make me feel energize but when i suddenly pressed down the volume down button it suddenly doesn't work. Should i go to the store where i bought my phone and exchange it? The first time the volume down won't work, it just worked after 5 minutes or so but suddenly won't work again. Then it just didn't work for two days. I don't usually use my volume buttons because i always use headphones plus headphones have mics on them. What do you think i should do?

Since this keeps happening I would suggest taking it to an apple store and have them check it out, it is most likely still under warranty so they will take a look a it for free and if it can't be fixed they will give you a replacement.