Q: iPhone 5c won't turn on/keeps shutting off

Ive had my 5c for over two years now and this problem I've been having with has been re-occuring for the last 8 months. It doesn't matter how much my phone is charged it could be 100% or it could be 25% and it will shut off completely. Sometimes i turns back on right after i plugged it in and sometimes stays shut off for hours and hours( even when plugged in) . It is to the point now where i have to keep my phone plugged up at all times so it won't shut off. Now its shut off and its been off for a little over 24hrs now. Ive had it plugged in all this time but it just keeps showing the low battery indicator... Ive tried holding down the sleep/wake button and the home button but nothing happens. Ive also tried hooking it up to my mac and trying to restart it that way but also no luck. If anyone can tell me how to resolve this issue or what is wrong with it that'd be greatly appreciated.