thanks for choosing health care majic.In any young adult this is normal.Normally semen is produced in the testis by body regularly.It is a continuous process and when there is sexual excitement it comes out.so it is absolutely natural.If your thoughts are all the time keeping your brain preoccupied with sexual thoughts you need to take care of that.Keep reading good books,do not sit alone,be creative.Other wise there is nothing decrease in power on anything like that.