There s nothing to worry about. There can be various reasons for irregular periods. Generally the initial few months after menstruation begins is irregular and may take time to normalize due to hormones. However it can be triggered by one of these factors such as:
a) Emotional stresses can also irregular periods.
b) Excessive weight loss or gain
c) Eating disorders like Bulimia
e) Certain medications like birth control pills
f) Increased exercises.
I would suggest you not to panic for one skipped period and wait till next month to see if you have got your periods. If it continues to be irregular, then you can consult your obg-gyn doctor.