Can you get us a decent picture of your guppy? A dark area, called a gravid spot, in a female guppy is quite common whether or not there are fry expected soon. I don't recognize what you mean by a white bubble thing by the anal fin but have seen 5teady's thread where he talks about something that would be called an ovipositor in egg layers appearing shortly before a fry drop. A clear picture would go a long way to identifying the stage of your guppy's pregnancy.