Hello Thanks for your query. You havent mentioned if you have been sexually active since. The first cause is obviously pregnancy or a related complication like a miscarriage or an ectopic pregnancy. Stress, weight gain, thyroid hormone disorders are other reasons. Viral illness, flu, fever ( the rash supports it ) also sometimes cause missed periods. Consult your gynecologist to rule out these, as well as other gynecological conditions such as polycystic ovaries, endometrial hyperplasia etc. Take care.