Why is my phone acting weird?

My phone sometimes gets turned of and on by itself and this happens nearly everyday ... it once turned off and on over 50 times like that isnt normal... when it finally gets turned on my messages get deleted , i get loged out on every app and its pretty frustrating ... sometimes my power button doesnt work at all and i cant turn off my phone ... it has happened to me that my home screen button doesnt work too ...every time i touch the button it takes screenshots ..and also there are these two things that appear every now and then and dont let me do anything ..one tells me to press the volume up and power button to restart my phone and so but if i do that my phone wont turn on for a pretty long time and then the other one is the menu of power off, restart and airplane mode and i dont even press the power button ...when these things appear my power button doesnt even work anymore ...HELPPPPP PLEASEEEEEEEEEEEE