Why Me?

Today I feel like very left out, alone and lonely.. I dont know why.. I have a lot of friends, and there has been a new addition in the family but there isnt anything that excites me anymore. When I see at other people, i feel all r so happy and enjoying their lives. Why am I cribbing always..? Why am I sad always? Why?? I am sulking every single day.. not knowing how to get over it.