In the absence of pregnancy
the most common cause for delay in periods is stress and anxiety as you rightly pointed out but there are other non medical causes like being overweight
,doing excessive exercises,after a illness or due to taking some medicines etc.
Medical reasons could include hormonal imbalance like poly cystic ovaries and other problem like hypothyroidism
Just wait for a week more and if you still don't get it,you must consult your doctor and subject yourself for physical examination and relevant investigations.
Once the cause is found,the treatment can be instituted which shall bring your normal periods back.