I Am Always Incredibly Tired, Eating Loads Of Junk Food

I am always incredibly tired, eating loads of junk food and gaining weight because of it, always moody or unhappy and I've been incredibly lacking in motivation, for example:

I have never ever handed college work in late, I'm always early, but recently I've just had the "can't be bothered, who cares" attitude.

My girlfriend is really worried and is noticing these changes too. It's completely out of character.