Hello, I appreciate your query. Sometimes, the urine pregnancy test ( HCG test ) is not completely reliable. It rarely gives a false positive result for eg. reading the test beyond the stipulated time period. Or, contamination of urine by some substance present in the container ( if a sterile urine culture vial was not used ) Evaporation lines are mistaken for a positive pregnancy test many times, particularly when adequate amount of urine was not added. However, the confirmatory test here is definitely your HCG level, which is negative. So you are surely not pregnant. To find out the reason why you have not had your period yet, please go for detailed examination by your gynecologist. Go for an ultrasound, rule out hormonal abnormalities of thyroid, prolactin or other disorders like Polycystic Ovarian Disease. Sometimes, exercise, stress, fluctuations in weight might affect the menstrual cycle. Hope this helps you.