Recently my periods have been brown and thick clots with hardly any normal red blood atall and lasting around 2-3 days. I have been on the pill for 2 years now.
I can't speculate on that but I do advise you to see your GP so that he/she can tell you one way or the other. A visit will put your mind at rest, anyway. Good luck.
I have alternating periods of "normal" and ones like you describe. I have never thought it cause for alarm before reading your post and others answers. I have been on the pill for 10+ years. Please do post on how you got on at the docs.