Modern pregnancy tests are very much sensitive and can detect minute amounts of pregnancy hormone esp. HCG in urine and blood.Virtualy the chances of being pregnant in absence of a positive pregnancy test are almost nil that too after 1 month of stoping ur periods.Keeping in view that birth pils,iregular cycles,resuming cycles after childbirth may b eratic and in early cycles after menarchae and even psychological stress can be a cause for the delay of cycles.Also one should keep in mind other endocrine causes of cesation of cycles besides pregnancy. You can be but the store test are not as accurate as the doctor office. Go and see your doctor and they will give you a more definative answer. If you have had major changes in your life lately with lots of stress, sometimes that affects your period or you could have another medical issue, like tissue build-up in the cervix that would cause the period to miss.....