Why is my phone on low battery and keep turning off?

Hi! I have a quite new Iphone 7, barely a month in my possession. It's been good so far (which is great, as the first one I had to trade in due to issues) but tonight, it's suddenly reached low battery and now it will turn on for only a few seconds before shutting off and saying it needs to charge, and then that process keeps repeating. For a few times, it showed my phone screen and I could use it, now it's only showing a black screen for the few seconds it turns on. It will not stay on long enough to restore using Itunes, to do the volume button+power button trick, or anything, so I guess I'm just looking for anyone's guess as to why it's doing this? Seeing as there appears to be no solution.

Prior to my phone starting this ghoulish on and off process, it had been at 3% before it just shut off on low battery. I charged it, it turned on for a few seconds and then shut off again, and thus the process began. I was browsing an app for a while. Could it be a weird virus, or is this just my curse with phones, now?