Hi, I'm 43, and I also have OCD.
I really don't see how leaking a little bit of semen when you pee could be related to an STD. Problems peeing, like trouble starting, or leaking pee in your underwear, can be a symptom of an STD (although a simple urinary tract infection is far more likely).
I also don't see any relationship with leaking semen when you pee and prostate cancer, which is almost unheard of at your age.
Your prostate is leaking some semen when you pee because it has no other way to discharge it. In theory at least, not releasing semen, over a long period of time, could increase your risk of prostate problems when you get older.
Short term, your decision not to masturbate will not cause any physical problems. But, in the long term, it might (or it might not) cause problems. Maybe you should reconsider the no masturbation decision.
But, as for leaking a little semen when you pee, that sounds perfectly normal for your situation.
hey I am a 17 year old guy as well. Though I still masterbate this still happens to me, it might be you have not ejaculated in a while but you should be fine.