What Causes Lighter Bleeding With Nausea And Tiredness In Menstruation?

Hi. I am 33 years old. 2 years ago after the birth of my son I got a non-hormonal IUD. Since then my periods have been fairly regular. However I started my period 2 weeks ago and it's still going. It has not been as heavy as usual, and the color has been a dark brown. I have also had nausea and been very tired. I started paxil and a blood pressure medicine shortly after starteng my period and was wondering if this could be part of the cause.