What Causes Brownish Vaginal Spotting And Pubic Pain Before The Periods?

Hello. I am 38 years old. I have regular periods ad I am generally fit and healthy. Just before my last period I noticed I was spotting very dark brown blood. This lasted a couple of days then I got a very heavey period which lasted for 3 days. Now mid cycle I am getting the dark brown blood spotting again. this is the first time I have experienced this. I have also been getting some pain and discomfort in my pubic bone area. What could be the cause of these symptoms?