The formal definition of Pre-cum is "Cowper's fluid" which is developed in the Cowper's gland. This fluid prepares the Urethra for the passage of semen and neutralizes the pH of any residual urine. So it does serve a purpose. The amount that a male secretes varies from none to a large amount. There are conflicting results that determined whether this fluid contains sperm or not. So I wouldn't count on withdrawal as a way of birth control.

I wouldn't worry too much about it. Try taking your time before climaxing. Tease yourself first. If you masturbate, stroke until just BEFORE you climax and stop. After doing this a few times, you just might see some pre-cum come out. If you climax too soon, you may never see it. This happens to me sometimes.