Hey, Kitten --
Yes, it is possible to have an STD even if you've never had any sort of sexual contact with anyone else -- the reason being that a number of STDs can be transmitted in non-sexual ways. For instance, many people have cold sores, which are caused by a herpes virus. If a person who has had cold sores performs oral sex on someone, that person can contract genital herpes as a result -- even if there weren't any cold sores present at the time. (The herpes virii are transmittable even when there are no sores present.) That's just one example of how it's possible -- there are lots of other ways.
So. Grab yourself some dental dams, or heck, just some regular plastic wrap (not the microwavable kind, though) and use it as a barrier during oral sex. And latex gloves are a good idea during manual sex, both because they prevent transmission of any STDs or other bacteria that might be floating around on your skin, and because they'll prevent scratches and such from fingernails.
If you look around the boards, you'll find some previous discussions on the issue of STDs even if you've never had sex, as well as some more information on why we suggest safer sex practices for all varieties of sex.
"The only unnatural sexual act is that which you cannot perform."
-- Alfred Kinsey