I was so certain that I wasn't pregnant

I was so certain that I wasn't pregnant. I was preparing to make a doctor's appointment for endometriosis because my. Had all the sudden become irregular and haven't started. I had taken a pregnancy test just four days earlier period that test was negative. They needed me to take another pregnancy test just to be safe. I wasn't really waiting for the results, because I was certain that it was negative. I was trying to think of a day that I could take off of work so that I can have an ultrasound. When the lab girl grabbed my arm and told me to look. I was sort of confused and when I look down at the test it said I was pregnant! I took a second one just to be sure! The second one was even clearer than the first. I am absolutely terrified, but very excited.