the feeling's gone, and i just can't get it back

it always comes back to this same feeling. i don't know why i can never stay happy, i feel like i always have to make myself sad. i do it to myself, and i don't know why. i don't think i like it. i don't enjoy crying to myself. but it just gets harder and harder to talk to people, and it's just so much easier to isolate myself. i can't understand why i do this, and why i've always done this. maybe it's just the routine of it all...i know what to expect once i start acting this way? i don't know