What Causes Irregular Menstruation Cycle?

Hi, I've had a few problems the past 4 or five months with my period.. I. Didn't have my period for a month, then I thought it was my period for about 3 days where I had clear discharge with little bood for a day, then it turned a nasty greenish brown. I recieved my real period a week and a half after that. My period was late by a week again this month and I found a white sesame seed looking ball while whiping.. should I be alarmed? Thank you