It doesn't usually start right away unless there's obstruction to the pelvis. Sometimes that happens, and it's a congenital issue, so that as soon as you have a period, you start to have pain. This is something that builds up slowly. The pain initially may be minor. Of course, this is normal; this is just what happens to girls. However, when it becomes so serious that they have to miss school, they see the school nurse.
Periods last five to seven days. If you are bleeding for 10 days or 11 days and you're having pain for all of that time, then you know there is something wrong.
You need to take a good history. You need to take a gynecological history, and for this you need time. You need to have some idea about endometriosis: pain, heavy bleeding—