lower left abdomen sharp pain and discomfort near hip

The period I just had had an unusually light flow (about half my regular flow, as a rough estimation) which lasted three days (one day less that my regular), and then this pain came the morning my period ended. I woke up with a sharp pain about halfway from my belly button to my left hip. It was intense, so much so that if the spot was any bigger I would cry, but for the rest of the day it was more of a mild, hardly noticeable discomfort. I'm wondering if this could be implantation bleeding and not a period. And if it is a period why it was so strange this time and, if this is a pregnancy, could it be ectopic or similarly abnormal? Soooo confused