I can't put my finger on what's wrong. 我不晓得什么地方不对劲儿。

I'm a bit down in the mouth today. 我今天有点闷闷不乐的。

I feel kind of blue today. 我今天有点郁闷。

I'm in a bad mood today. / I'm moody today. 我今天心情不好。

I am in no mood for joking! 我没有心情开玩笑！

I've been down in the dumps recently. 我最近很郁闷。

Sorry, I got up on the wrong side of the bed today. 抱歉，我今天心情不好。

I'm so down. 我心情很低落。

I'm so depressed. 我很郁闷。

I feel low today. 我今天心情（有点）低落。

I feel so upset. 我觉得很沮丧。

I am not in the mood. 我没有心情。