I Got Bleeding Only In One Day(on 26th Day).after 2

i got bleeding only in one day(on 26th day).after 2 days i took urine test but it was negative..again after 3 days took urine test it was also neative.then went to see doctor.she took blood test .that was also negative..Dr gave dupahston for 5 days .i had duphaston for 5 days.waited again 5 days.but no period.today again took urine test .but its showing negative..