Missed Periods/Light bleeding?!

Well I currently have been having irregular periods since September 2010. I had my period September, and didn't have it unti January 2011, and now again it seems that this month I only have had spots. I am worried because I am not sure what my cause is. I am definitally not pregnant, and not aneroxic. I also am a pretty happy, and I eat healthy and get regular extercise. One thing to mention is that recently I have lost a lot of weight due to dieting and changing my lifestyle. However, I still cannot figure out the connection to my problem. I eat wisely, and do not use any dieting prouducts or such..Well I would really appericate it if someone shared a bit of their knowledge or experience with such problem as myn..