iPhone 4s not charging.

Okay so my i've had my iPhone for almost a year now. My phone has been working just fine after the iOS7 update (except for the fact that my phone battery drains very fast). The charger that came with my phone completly fell apart and wasn't working so I threw it away. a few weeks ago, I bought one of the cheap iPhone chargers from Fred Meyer's. it worked just fine... I even charged it today and it was perfectly okay. Next thing I know, I go into plug in my phone and I noticed it wasn't charging. I thought it might be the wall plug in piece but it wasn't. I thought it has to be the cord. When my phone fully died, I plugged it in and it was charging, but once it turns on again, it's not charging anymore. PLEASE HELP ASAP!!!