Why bleeding when is not yet my period

Menstural irregularities 
Menstural cycle is a normal physiological process that happen to every female adult who have normal ovulation as the hormonal changes that happen during the cycle beginning with estrogen stimulation of the endometrium to develop partially then the ovulation happen so the ovum begin to secrete progestron which stimulate the endometrium to develop completely and get ready to receive the fertilized ovum, if the fertilization happen then the bleeding will not happen and the pregnancy proceed but if no fertilization happen then the endometrial shedding happen and the bleeding occur. In some cases of ovulation disturbances the cycle will be irregular and the bleeding will not occur at the expected date so a through investigations should be done if the bleeding did not occur on time and you should consult a gynecologist 
Investigations 
After proper physical exam, You should hormonal study including pregnancy test if you are expecting pregnancy by doing serum test 1 wk after the delay or urine test 2 weeks after the delay in bleeding. Other hormonal tests are FSH, Estrogen, Progestron. Serum glucose testing to detect any rise in blood glucose . Thyroid fuctions TSH, T4 to detect any thyroid dysfuction. Pelvic ultrasound should be done to detect any ovarian polycystic disease and to check for any uterie anomaly.
Causes 

• Pregnancy 
• Polycystic ovarian syndrome 
• Uterine anomalies 
• Thyroid dysfuction 
• Central cause of hormonal abnormalities 

Our advice 
You are adviced to have a diet which is rich in vitamins and minterals from its natural sources, reduce your weight to ideal and have regular exercise in addition to smoking cessation