What Causes Delay In Periods?

hello, i m a newly married lady, hv been taking elogen from past 3months.. and never missed my period..

Every time i get the menstual cycle on the same day. this time its been delayed by 2 days and im very afraid if i got pregnant..pls help me.. also plese let me know how to find out pregnancy in the first week of conception. we dont want to become parents this soon. Kindly help..