Usually, If a women miss her period first thing crack mind is pregnancy. So, always wait for post 5- 6days missed cycle and take Home pregnancy test. if it comes negative, then it will be good enough if you talk to your doctor.. There are some other reasons for missing cycles like- Breastfeeding, Stress, Illness, Weight, Excessive physical exertions, Changes in daily schedules, Medications, Hormonal imbalance, Thyroid disorder, Perimenopause etc...