help can't get wet?

I can only get wet watching porn. like on a day to day basis I really don't have discharge and my underwear never gets too dirty per se. Even when I'm horny it's still dry as hell. I'm still a teenager (18) so why is this happening ? I need lube for intercourse . But porn or any good sex scenes I have no problem getting wet and self lubricating. Even when I ovulate I'm barely wet. Yes I drink a lot of water and eat healthy, take vitamins and the doctor said my health was good .I'm also very active. Could it be my hormone levels or a perhaps a thyroid problem? this was never an issue when I was 15 and under. And I didn't become sexually active until this year so it's kind of a really annoying nuance