I'm not pregnant I did a pregnancy teste and was negative, why am I so late, almost a month, im staring to worry ; (?

Stress?? thyroid?? There are many reasons you can be late. First, has your cycle always been regular until recently? If so, have you lost a lot of weight recently? People with low body fat can miss their cycles, or have you maybe gained some weight? If your thyroid is not active enough, you can gain weight and your cycle can be irregular. Also, if you are under a lot of stress your cycle might be irregular.
Anovulatory cycle? You may have had an anovulatory cycle which can cause menstrual irregularity. Pregnancy tests are very sensitive but not perfect. See your physician if you are concerned.
Retest. You may have tested too soon. Retest, if still negative see your doctor.