its good that u aware of nocturnal emissions are natural one,in similar way when it happens early in night when u in deep sleep,not aware of it-its get dried up throughout night... so its absolutely normal....
whatever u experiencing in nighttime is called nightfall... its normal in this age group...this is increased because u stopped masturbating.
Like urine and stools,semen also made to let go out of body...as it collects it passes through ur penis periodically and automatically.
safest way to stop this is masturbate regularly if u comfortable with it.(masturbation
is healthy and safe outlet for semen outlet and to decrease embarrased feeling of nightfall..)
still u concerned about it meet psychiatrist