Well from what you are describing there can be a number of conditions which can cause this sort of brown vaginal discharge, the first one which comes to mind is that you could have a mild infection in the reporductive tract. This can be present even without the typical symptoms of fever, abdominal pain etc. Infact many low grade infections usually only present with an odorless discharge. It can however cause urinary symptoms which may be mild such as frequency or burning in some cases. The first thing to do here would be to get urine tests including a simple analysis as well as a culture done. A High vaginal swab should also be done to determine if the discharge is infected and a plevic examination. If needed an ultrasound can be done later on. This would be followed by a course of antibiotics to clear this up.
Now while you do have an IUD in place and it should prevent a pregnancy in most cases but it is not foolproof, there is a very miniscule chance that you could be pregnant. The chance is about 1% or even less than that however it is present, if an infection is ruled out then a pregnancy can be considered even though chances are that you are not pregnant. But a brown discharge just before your period can be associated with a pregnancy or even a miscarriage. This can be a cause of the brown discharge.
Another cause of this can be uterine or cervical polyps. Uterine polyps are also called endometrial polyps. The Polyps can cause a discharge as well as bleeding after intercourse, heavy menstrual bleeding, and abnormal vaginal bleeding. However if they are small in size that can lead to a small amount of brown vaginal discharge without any of the other commonly associated symptoms.
Now in your case since this has been going on for a week, it should be evaluated with a pelvic examination and other tests which i have mentioned above. If it had stopped after a couple of days i would have not advised a visit to the OB/GYN but since it has been 7 days and it is consistently occurring then a pelvic exam and a ultrasound is certainly indicated.
Do you have any more questions?
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