Nocturnal emission(semen getting released at night/night falls/ wet dreams) is also recognized as involuntary ejaculation, and it occurs during sleep. In addition, it is a completely natural process of the body that takes place due to many reasons. Moreover, involuntary ejaculation is completely normal, and it acts as a spontaneous orgasm to satisfy the intense needs of the body. And, this process is more common in teenage males. Also, it is an important process for the development of reproductive organs of an adolescent male. Furthermore, the reason for nocturnal emissions is that the body of a male is partly designed for involuntary ejaculation since a male need to ejaculate reproductive fluids from time to time.
The most common reason for nocturnal emissions is romantic dream imagery. Furthermore, when a male gets too much involved in the thoughts of lovemaking, the amount of testosterones increases that stimulates the production reproductive fluids. And, the reproductive fluids get ejaculated through involuntary ejaculation process when the reproductive organs are unable to hold the excess amount of fluids.
I would recommend you to avoid over-stimulation of your genitals, you should take the initiative to self-control, avoid reading an adult magazine, TV, pornographic websites, and try to make efforts to overcome the habits of sexual fantasies.
Try to involve your spare time in sports, meeting friends, actively participate in cultural and other activities. all these efforts will help divert your attention from the sexual fantasies and this reduce the frequency of night falls/ wet dreams.
If in-spite of all these efforts you still experience the same frequency in nocturnal emission I would recommend you to discuss it with your parents and seek appropriate consultation.