I think you are either excessively afraid of pregnancy
or very much willing for that!
In first case you have a stress
that may lead to amenorrhea/lenghthening of the cycle, in later case rarely ladies develop Pseudocyesis-where patient feels she is pregnant but actually she is not!
I would advise you to repeat the urine pregnancy test and get one ultrasound
abdomen just to cover a laboratory error!
That will sort out this problem definitely.
May you get a good health.