long period

Hey girls!I have doubts...since February my periods are regurarly after 17 days and they start with 4-5 days of light dirty stains and after 5 days I normally begin to bleed properly and then it takes for about another 4 days to get my period finished!so my period lasts up to 10 days!! Its annoying...does any of you have the same problem??Im going crazy and dont know what it can mean...my doc said it could be due to stress but I dont feel stressed...any other explanation???thank you ladies...