Help: My 3DS Keeps Turning on by Itself When I Switch It Off

I've been having some strange problems with a New Nintendo 3DS XL that I bought second-hand over a month back. It's been perfectly fine until last night, where it started having problems with switching off/on. It takes a while to switch off, even after holding down the power button, and when I do that, it skips past the 'Power Off' screen and switches off. After switching off, it switches on by itself again within a minute.

The power button in general seems to be unresponsive, otherwise everything in console (including all my games) run normally. Not really sure what to make of this, can anyone tell me what's up? I feel like the power button has gone bad, but that wouldn't make it start up again constantly, right?