What Cause Brown Blood Discharge Before And After My Period?

Over the last 4 months I have experienced brown blood several days before and several days after my period. This month I had 2 periods (for the first week of the month and then the 3rd week of the month). Now, more often than not, I have a brown discharge (it seems to be a daily occurance). I do have an IUD and am concerned it may be causing problems or something like endometreosis which my sister has. Any ideas would be greatly appreciated. Thank you.