Hi and thanks for using the forum.
Well, you could wait and see if your period actually starts this month. You could also re-test to be sure you are not pregnant. IF the pregnancy test is still negative, then most likely it is accurate. It is not unusual to have an "off" period every now and again, so you could wait and see what is going on next month. If you are concerned however, you could call your OB/GYN for an appointment to put your mind at ease. Good luck.
Bridget
Haven't been sexually active for a month and a half* had to correct it sorry