Need advice.... My 14 year old's periods begun about 2 years back, the first year her periods were pretty irregular (periods coming once in every 2-3 months). Since the last 1 year, it has regularised to monthly cycles with a normal flow lasting about 5-6 days. However this month, though her periods began on time, the flow has been very scanty & the blood is dark (black) & thick instead of the usual bright red & liquidy flow. Could this be due to stress... due to her ongoing exams?  Is this common in teenagers in the initial years of menstruation? Should I be worried?