I had a blood test when i was 8days late and a urine test and it showed negative, i am currently currently 15 days late and never missed a period b4.

It happens sometimes: In a woman with regular periods, some causes of a late period are: excessive weight loss or weight gain, increased exercising, emotional stress, having an illness, traveling, medicines (like birth control pills), hormonal imbalances, etc. Seeing a doctor is a good idea if symptoms are persistent, recurring, or worrisome. Pregnancy is a common cause of missed periods, but not if negative tests.