My phone keeps unplugging itself

A few months ago, my charger broke so my dad had bought me a new one from Metro PCS. That stopped working a few weeks later, so I got another one. I've had it for a few weeks now and it did fine, but now for some reason it'll randomly stop charging by itself. Now, it's an easy fix in the moment. All I have to do is replug it. But this gets really annoying when i leave expecting my phone to be charging(let's say, while I'm sleeping and waiting for an alarm for example)

Any clues on how to fix this would be great, thank you!