A cone biopsy usually has nothing to do with the delay of your period. Additionally, a negative pregnancy test excludes pregnancy as a reason for the delay in menstruation. Period delay can be due to reasons other than pregnancy. One of the most common reasons is the persistance of a functional ovarian cyst. You may request a vaginal ultrasound to find out if an ovarian cyst is, indeed, present. If there is a cyst and the cyst is not larger than 5cm, you should wait for 2 cycles and observe the menstrual cycle again. Small functional cysts usually disappear spontaneously. If the cyst is larger than 5cm or if a smaller cyst still exists after 2 months, it has to be removed. You can go to your gynecologist for an examination.