Yesterday, today and tomorrow

Why am I sad today? Is it because I am wishing for a happier tomorrow but I sense that my tomorrow may not be happy? Is that the reason why I'm making my today a sad day as well?

About a year ago too, I'd wished that I have a happier tomorrow. But today, which is yesterday's tomorrow, is not a happy day. So I feel that my yesterday's sadness was not worth it. If only I am happy today will I not have to worry about whether I will have a happy tomorrow because atleast by being happy today I would have made my yesterday's tomorrow a happy day. And tomorrow's yesterday too :-)