What Causes Irregularity And Brown Thickish Discharge In Periods?

I am 19 and I have been having my periods for 4 years.during these 4 years they have been irregular,I would skip a month or sometimes twice in one month.at a certain point they were controlled by my emotions.they last 4 days or 6 at most.recently I missd fr 3 months and instead of blood there was a brown thickish discharge and dis month I had a period like episode but the blowed looked brownish red! Should I be worried?