Why is it that i haven't got my menstrual when both of the pegnancy test i took came out negative?

Lots of reasons: There are several reasons women miss periods. Some are pretty limited and easy to get over like stress. Hormone issues can also delay the cycle (thyroid, adrenal hormones). If you are making too much or too little estrogen, you can also have irregular periods. If this is new for you, you should see a doctor. If you ever go more than 2 months without a cycle you should see a doctor.

Timing important too: Agree with dr b. Also important *when* you did your pregnancy tests. If you took a home pregnancy test done less than a week after your missed period, it could have been too soon to show up on the test. Blood or urine pregnancy tests done at the doc's office/lab can detect pregnancy earlier than that.