Does endometriosis pain get worse when you have your period?

Possible: Endometriosis is presence of uterine tissue outside the uterus. It behaves the same as the one inside the uterus So during the period it starts bleeding where it is sitting. This might cause increasing pain during the period.

Yes: The endometrial glands that are not in the endometrial cavity ("endometriosis") bleed and shed the same time as the endometrial ones, except they're trapped where they are (in the ovary, in the abdomen, in the lung, etc) and causes pain by mass effect. Later, as that tissue gets trapped long term the body sips it up and it becomes scar tissue.