Hi..... I Am A Woman....34 Years Age.... I Have Problem

Hi..... I am a woman....34 years age.... I have problem of my mensus ( monthly periods ) this problem was start about 8 years ago.... Before during this period.... I had 5 days bleeding.... But from 2008....only 3 days.... But now about one year....it becomes only ....1 day or you can say only 24 hours..... Also before start this 1 week my back pain comes and during this period no feel any thing....but after finish this...again one week back pain same that I can not wake up from bed.... I have not any baby.... I was my check up from Doctor....but she says that....no have any problem for baby and about mensus she tells me that this is the problem of changing in Harmons.... Please can you help me in this matter?