You have not told us your menstruation cycle. Have you been getting your periods regularly in the past? Has it happened earlier ….you missing your periods? You have not told us your age.
One very important reason for missing periods is stress. The brain has an area called the hypothalamus, where hormones are regulated. This area can be affected by stress. The more you stress out about being pregnant, the more this area is affected. But stress need not be only about sex, it could be a death in the family, or fear that your boyfriend may breakup with you.
Nature has a way of protecting you from getting pregnant if your body is under such extreme stress. Your body prevents ovulation so you don’t have a lot of estrogen, don’t build a big uterine lining, and then don't get a period.
You have ruled out pregnancy as you have done the Test. So relax. Did you take any emergency pill after the sex? Ipills are known to cause disruption in menses cycle.
Have you had a major weight loss recently? This can affect periods.
You have told us that you have PCOS. How did you find out? Did you get this confirmed with the Doctor? This is the most likely cause of your missing periods.
PCOS is a hormone imbalance that results in lack of ovulation. You have altered levels of estrogen, progesterone, and testosterone. This can cause you to completely miss your period or just not menstruate regularly. Other PCOS symptoms include hair growth in places like the face and chest, difficulty losing weight, and potential fertility issues.
You must see the Doctor. He can help you come up with a treatment plan to manage the condition. You need not tell him that you had sex, thoughh if he/she examines your vagina they will be able to tell that you are not a virgin.