Hello Thanks for posting your query. You can sometimes have lighter periods than normal. Do not worry about it. Your hormones can sometimes play up, especially if you are worried or anxious about something, maybe exams or family/friend problems. So, to have a one off irregularity like this, is not unusual. Hopefully your next period should be normal. However, if your next few periods continue to be light or delayed, you may need to see a doctor. For girls who are overweight, or grossly underweight, ovaries may not function normally, causing period problems. Your doctor may want to do some tests and give you general advice about diet, exercise and so on. As for now, do not worry. This kind of one off irregularity is very common in girls your age. Hope that has put your mind at rest. Best wishes.