Lack of my period

everything i have read about irregular periods always say its normal for the first year or so, but it has been over 5 years and i am still very irregular sometimes not having it for 6 months or more at a time. when i eventually get it its either very very brown/black in color or will come for a day and then go away and not come back for awhile. could something be wrong. Could endo. be a concern for me? thank you andy