I think you having minor depression. When a person started to have depression, they cannot sleep or cannot sleep well, unstable mood, suddenly laugh or cry. You need to see the doctor to give you sleeping pill and refer you to the psychiaterist and they will give you 抗抑鬱藥. You cannot buy it from drug store.
If you have some good friends, you need to communicate your someone who love and care about you. You need a good listener and a good adviser. You need to express your feeling, try to think more positive and try to do something you like and enjoy, make yourself more happy, then you feel more joy and sleep well.