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As you got periods in 28 days then your cycle is normal in case of number of days.As far as bleeding is concerned if you have proper bleeding for 2-3 days also it is normal.The only thing what I guess from your weight of 45 kgs is that you may be a bit underweight
and if I am not wrong you may even have anaemia(that is less haemoglobin
).If you are not sexually active then there is no reason you should get worried about the 1 day period and the brownish bleeding with tissues.The reason for such a cycle can be anaemia;hormonal
in ovaries(PCOD).Please visit a Gynaecologist and get examined.If necessary she may advise you Ultrasonography
of Pelvis to see if you have any problem internally and if needed she will give you the needed treatment.