What Causes Delayed Period While HPT Is Negative?

                                             hello, i am having problems with my periods and i do not know if they are irregualar or not? i weight 55 kilos, i excerise 5 hours 4 days a week, i smoke a packet of fags a day, and alcohol i drink at the weekends, i am now 2 weeks late for my period and i have taken a pregnancy test and it has come up negative, but it says to wait another few days and try again and i will try again but i would like some answers as what could be happening and if there is anything i can do. please help me. thank you.