It is right that these are urethral secretions and not semen. Every boy and man has erections 3-4 times at night, during which urethral glands produce this. If it is more, it comes out of urethra, otherwise it gets dried up in it which passes when you pass the first urine or sit for stools in the morning. It also comes out when you think or fantasize about sex. This is absolutely normal. Stop any medicine to cure this as this is not a disease - in fact it should come - that is the proof of your normalcy.