How do I shut up the negative little voice inside me head?

Kay, so I'm in a fairly good mood right now. I'm happy and I feel positive things, but at the same time there's this silly annoying little voice inside my head that won't leave me alone. I say 'i love my life' and then the nagging feeling will be like 'no you don't' or I'll be thinking this school year is going to be fantastic and then I'll have this stupid doubt in me. How do I shut that negative voice up?? I want to be happy and free!