False-positive pregnancy

Is there a still a chance or possibility of a false-positive pregnancy even after getting 3 times positive result in PT and 3 months missed period? Or it is really confirmed that you are pregnant? Because I've read an article that even if the PT result shows positive pregnancy there is a chance that you are not really pregnant, and I don't wanna get disappointed. Haven't had my ultrasound done yet because of the fear that I may not be really pregnant.