Are you taking any medicines?
While embarrassing, this problem is actually quite common.
There are two potential causes:
1) A soft diet causing soft stools or a diet high in caffeine. Soft stool can periodically leak out of the anus. You said it was clear fluid, this sounds like it's the natural secretions of the anus, and not stool. Thus, I think it might be --
2) Hemorroids. These are veins that occur normally in the anus. However, when engorged, irritated, inflammed or otherwise very large, these veins can actually interfere with the anus closing properly. This allows fluid to leak out.
Try these links and Preparation H might help. If not, I recommend prescription-strength medical and a rectal exam.