What Causes Delay In Periods And Being Diagnosed With PCOD And Hypothyroidism?

Hi doctor,i am 31 and a mother to a 3 yr old. I ve pcod and hypothyroidism. Im taking thyronorm 125 daily. I ve been trying to conceive again and was put on metformin 500 twice a day, folic acid and meprate 10 mg frm the 14th day of my cycle fr 10 days...in october 2014. Eversince my cycle has been regular as i ve always got my periods maximum by the 8th day of stopping meprate. This cycle, its been 12 days already n no periods still...i ve done two hpts but both r negative. What can be the cause of this? Could i be pregnant even after these negative tests?