iPhone SE problem
It has now been 17 weeks that my phone has not backed up . Could it be the reason why my phone it Turing off and on automatically?
Question marked as
No. Backing up or not backing up has no relation to your iPhone turning on or off.
However, your iPhone continuously turning off, may be interrupting the backup process and not letting it complete which may be why it has not backed up in 17 weeks.
Try backing up to a computer, (How to back up your iPhone, iPad, or iPod touch with iTunes on your PC - Apple Support) and then take it in to an Apple Store to get it checked out: link-> iPhone Repair - Official Apple Support