On and off period, endometriosis

Hi girls, basically I've been having really strange periods recently, I'd say probably for the last 3/4 periods I've had has been quite strange compared to usual, so I get dark brown spotting for a day or two before and then when I get my period is heavy, like extremely heavy to a point where this period in one day I used half a box of tampons, then the next day it's gone like absolutely nothing & then it comes back but extremely light and barely there, I've no clue what's going on because I'm used to really heavy periods due to my endometriosis. If this has happened anyone, please help!!