Well, you could stop going online!!
Paranoia is really common if you think or know you've been exposed to an STD. Even once you're diagnosed. I was diagnosed about 6 months ago, and I still freak out over every little itch, simply because all of a sudden I think I'm having an outbreak.
I'd recommend getting tested, for every possible STD. Once you know you are negative (or positive, I suppose), you can continue with your life in a slightly more relaxed manner. Just remember to practise safe sex in the future. It's not a 100% guarantee, but it sure helps!!