I am 30 and I have always practiced safe sex by using condom, except for receiving occasional blowjob. Two ago, I did HIV and STD test and the report came negative. Haven't had sex since then but I have indulged excessive masturbation habit. While watching a sizzling movie scene, I just noticed discharge of white fluid like milk. It was not smelly though. Also, it was not pre-cum.

1. Could it be chlamydia or gonorrhea transmitted from oral sex?

2. How can we distinguish difference between discharge due to excessive masturbation or due to any STD?

3. What should I do?