IPhone 6 Plus boot loop

About two months ago my iPhone 6plus started giving me major problems. I'll go off randomly, struggle to start up or even pass the apple logo. It's then stuck on a boot loop. Sometimes I have to turn it off my holding the home and power buttons down then the phone will black out, go to the Apple logo ( still holding the buttons) it'll go off and on again and only after that it'll turn off ( I have to hold the buttons while the phone reboots twice before it shuts off )

It's a struggle when I'm busy on my phone with something important it'll go off ( hard restart doesn't help it ) I can't update my phone, I can't backup and restart my phone because it goes off and on all the time even on recovery mode. HELP