Need help with spawn point

Im not sure why but my spawn will randomly switch to the nether like ill go somewere sit for a while come back and do /spawn and it will take me to this place in the nether? Also the warps do the same thing! Im so confused. Also do i need to install some world plugin that seperates the nether and end or somthing? Thanks for help in advance.

Skype- crush.mikey