How come it's harder for me to get happy?

Like that feeling of greatness and elation is what I'm lacking. I've felt it before so I know what I'm talking about. Lately, alot of stuff is happening to me that is wonderful, like going through diffucult ignments, getting enough relaxation afterwards, having enough food to eat, etc. And yet, I feel irritated somehow and I am still not entirely happy and this feeling sucks so damn bad. I don't know why. People can sense this as well and it sucks badly. Why is this? What is this?