thank for your query.
If you did not use birth control sincerely, and you had unprotected intercourse
meanwhile, then yes, there are chances of pregnancy
The period pattern you describe could be erratic on account of an early pregnancy.
Taking irregular birth control also causes abnormalities in your menstrual cycles.
YOu should repeat your urine pregnancy test to confirm.
Better still, consult a gynecologist for a definitive opinion
Also, switch over to a safer , more reliable contraceptive