Why aren t my earphones working with my iPhone?

I just got a new iPhone 6s 2 days ago. I tried the earphones that came with it at the store, and they worked fine. Yesterday, I tried to use them and, they didn't work with the iPhone, but they did work with my iPad. Today, I tried them again and, only one side is playing very faint music on high volume. I had the earphones plugged in all the way. Is there anything I could do to fix this? This happened with my last iPhone, and I was kinda excited to have a working headphone jack. Is there anything I could do instead of going back to the store?

This is very weird, have you borrowed your phone to anyone? They could have trolled you. Go to settings/music/ and check if the option volume limit says off. Then go to setting/general/accessibility and scroll down to a setting where you can put all the volume to one channel or the other and leave it in the middle.

If these were off and in the middle. Have you tried with other earphones? If you have a case on, are you sure you earphone jack is fully in? And if so, try to restore it. If that doesn't work, take it to the shop and explain your problem. If it is indeed a hardware problem, they'll replace it.