What Does Erratic Flow And Color Of Blood During Periods Mean?

Over the last 3 months I have noticed that my periods have gone from being basically normal with the normal red blood starting heavy and going light last 5-7 days and now it has changed into starting light going to medium for one day and back to light lasting 4-6 days in total and it is dark brown blood that looks like melted (the cooled) chocolate. is this normal? could it be a sign of pregnancy? should i be seeing a doctor? I have gone through alot of stress over the last 3 months but most of it has been resolved and I am feeling alot less stressed, but still stressed. I'm confused and scared. please help.