Delay in periods by 7 days. In periods.

Hello Dr., My periods are delayed by 7 days which is usually very regular. Last week around diwali time, i felt lightheaded as if i am loosing slight balance. Also, i slept a lot around 12-15 hrs a day(including night and afternoon sleep). It was an unusual feeling. I doubted pregnancy so i tested twice in 10 days but the test was negative. I am not feeling lighted headed any more and my sleep is back to normal. Not sure if those symptoms were due to taking holidays after hectic work schedule or something else. Also, since many months, i am experiencing a lot of hair fall and re ocurring dandruff even after using medicated antidandruff shampoo regularly. Hair hv become unusually dry. Not sure if these problems are related to each other. A couple of months ago, my vitamin d and b12 were very low so i took medications prescribed by the dr. For these 2 vitamins. i hv completed the course. Kindly advise what could be the reason behind delay in periods.