I spotted (brown) for 18 days. what could this mean? i have pcos and rarely spot or start a period on my own.

PCOS: I assume you are not on birth control pills. The follicles in your ovaries seem to be producing enough estrogen right now to build up the inner lining (endometrium) of your uterus and because the lining is shedding you are spotting. You probably want to take birth control pills strong enough to suppress the growth of follicles in hopes of avoiding to get the PCOS get worse.