What Causes A Delayed Period, Constipation, Abdominal Discomfort With Headaches?

i am 6 days late for my period, i have had constipation, some lower abdominal miscomfort from time to time, slight headache everyday...i took a pregnancy test yesterday and i came up negative...could you tell me if i should wait and see if i get my period or should i go to a doctor and find out whats wrong or am i just worrying about nothing