You would need to go to the doctor to figure this one out. Its nothing that anyone can help you with online, unfortunately.
Are you sure it is pus? It is normal for a woman's vagina to slough off liquid that is whitish. During ovulation it is clear like raw eggwhite, and other times it is cloudy and not as sticky as eggwhite. If that is what you are referring to, it is normal. If it is greenish and smelly, then check with your gyn.