Monkey brain, how to get over it?

so you know you have to do something, but you drag your legs and you feel distracted and you just can't complete the task you need to do. Stuff like school work or tasks at my job. Feeling demotivated and lazy lately. My brain doesn't seem to respond to things like money or gifts, I use to be able to buy my self nails or other stuff for getting good grades but now I don't care. My brain only responds to 2 things: hunger and pain. I considered asking my brother or friend to punch me in the stomach or something but I would rather handle the monkey brain myself. any suggestions? I can't seem to just force myself to do what I need to do.