I am having brown discharge and brown light bleeding since 5 days. what can be the cause?i am worried.have little backache too.

So many things: So many questions: how old are you? Could you be pregnant? Could it be a vaginal infection? Could it be your cycle getting started? Unfortunately, there are a lot of questions to be answered before i can really try and narrow it down for you. Bottom line: if it troubles you, see your doc. Good luck!

Last period?: It would be helpful to know when your last period was. However, what you are experiencing is not normal and you should see your gynecologist to find out what is going on.