What Causes Brown Vaginal Discharge And Nausea?

I m 25 years old. Not sexually active, not on birth control, never been on birth control and don t have any kids. I don t take any medication either. For the last 3 years, I ve had my normal periods at the end of each month, then about 12 days later I ll get a clear mucus discharge followed by 2 or 3 days of heavy bleeding woth no other symptoms but nausea. The nausea will fade after those 2 or 3 days the bleeding occurs, but I will have brown discharge for the rest of the month until my period starts again at the end of each month. It has to be something to do with my hormones, I m assuming? What can I do to help this?