I think you're okay too!
If you've only been with one girl, and she hasn't been with anyone else, then I think you're right, std's are outta the question.
It might not have been the result of not showering for a weekend, I know that sometimes guys just "happen" to get things like that.. If I can find specific information on it, i'll post it in here.
But if you're not having any weird symptoms, then i'm sure you're fine. It's important to shower nonetheless *shakes finger* lol, make sure your boxers or breifs or whatever aren't too clingy, and that you give your "area" some time to breathe.. Cause I know sometimes that can cause irritation.
Seriously though, it's all good, keep an eye on it, and if I get that info i'll edit this post.