What Causes Heavy Bleeding During Periods?

Hi im 24,6.5 in height i my baby was born Dec 2010,since after birth ive been on the mini pill where i got my periods once a month for 7 days, then on a generic one calld hayen,but i got my periods the begining and at the end of each month,7 days. I went back to the regular mini pill(stil breast feeding) ,got my regular once a month,until this month i got it for 7 day heavy bleeding then 5 days later i got it again heavy bleeding,changn 4 times a day..i bleed allot till the sixth day but usually its fades to a brownish colour by the 5-7 day. Should i be concernd. Thank u!