iPhone 6 won't charge or turn on

About 5 days ago my iPhone 6 was acting weird (staying at 100% all day then dying at 70% and charging to 100% after a couple of seconds of being plugged in), so I powered it off and left it alone.

But now for the past day or two I've been trying to get it back on by charging it, force restarting it, going onto iTunes on my PC yet nothing seems to work.

Any help is appreciated.

Note: I just got my iPhone's battery replaced 6 months ago.