What Causes White Discharge From Penis During Urination?

i have been masturbating for the last 3 or 4 years, and regularly, but nothing has happened to me until now, but yesterday when i went to the toilet and was about to shit, some kinda white liquid came out of my penis, and that was about two to three drops, and now it was the same today, Dr is this a problem or not, or if it i a problem then what should i do, Note: i have only experienced this thing in the toilet two times in two days, when i think of sex during daytime, and then when i go to he toilet this happens. !