Ill just have issues sleeping

Ill just randomly get where I can not sleep every now and then. There seems to be no link between what im doing and the sleepless nights. It will just be suddenly I cant get to sleep at all for the entire night. I dont even get sleepy. And then the next day I am stuggling to stay awake at work. Often times when i get home after struggling to stay up at work I again cant sleep that night. And then everything goes back to normal.