I am having a missed period this month, it is 16 days more than my expected period. I took 2 urine test which both says 'Negative'. I can't say about symptoms as I am not sure about them, I am having cramps in stomach, stress, vaginal discharge. At the end of last month I was suffering from flu and had to take a lot of antibiotics. I am really confused what to do? Normally my periods are regular. Also, I had an overseas trip last month for 15 days. Does environmental changes effect the menstrual cycle.