Pre-cum is not white; that is only the coloration of the semen, when produced in and ejaculated from the prostate. At 18, you shouldn't be needing porn; if you are in a relationship, value that... or you are dis-valuing both your partner and yourself. It's possible you had a spontaneous emission, but that would usually be accompanied by muscular spasms of the prostate also, and rather well-felt. Consult a urologist. Hope you have not waited since July to pursue this....