What Causes Prolonged Period?

i have very regular period and it usually lasts a week but this month it came a week earlier than i expect and it hasn't really stopped since. it's about the 3rd or 4th week now. i haven't been to the doctor's yet as the flow is not intense and for the past week it's more like spotting but it's a bit puzzling because of the consistency - it's dark in colour while sometimes it's really pale like it's mixed with white discharge. there's also clotting. i'm worried as everytime i feel like seeing a doc it stops momentarily (one day) but in the end it's a false alarm as there would be spotting later. should i wait and observe?