First, you need to undergo one home pregnancy
test if you involved in sex in the last month. Period late up to 7 days is considered as normal thing.
Other reasons are stress
imbalance, improper diet, over weight etc. Jet-lag also can cause late period as you travel for 15 hrs.
You would take health diet and drink more water. Avoid mental stress and take adequate rest. If you don't get your period within 2 to 3 days, you must consult with doctor for next management.