Cyst or Endometriosis?

Haley
Hey guys.
So I've been using this app for over a year now and have noticed a weird pattern. Each month changes from a 28 day cycle to a 38-41 day cycle.
Example: 28, 38, 29, 41, 28, 39, etc.
I've gone to several doctors and they always say I have endo but don't want to test for it because "there's nothing they can do." 
My shorter periods aren't normally bad but the longer ones consist of extremely painful cramps and most of the time I throw up from the pain. 
I never know what I'll end up getting. 
So has anyone experienced anything similar? 
I also have a retroverted uterus and can 100% feel it when I'm ovulating. It's very sharp and sudden pains.