I'm so sorry to hear you're having a crap time. Similar thing happened to me, I'm 24.
Until the end of this April of when I had an op I'd been in a pretty bad way, in a lot of pain - a&e visits collapsing in pain, i just couldn't do anything, since July 2014
I must have gone back to the doctors every 2-3 weeks, at first they thought it was ibs and gave me treatment for it but nothing worked. Eventually they sent me to a bsge approved gynae. They did an ultrasound and found nothing but I begged him to open me up and when he did I was covered in the stuff and have adenomyosis. A 30 - 45 min op took 3 hours! Now I have access to a pelvic pain nurse, more treatment options and early help with pregnancy etc.
Just keep keep keep pushing. My doctors is a practice so you can see any Dr working there which was useful when one was out of ideas. If yours isn't like that try going to another doctors if you can, some as you might find, are more reasonable than others - some have bizarre outlandish ideas about endo and its sufferers! Hope you never have to sit in a room with one of them!
I did a lot of research about symptoms of endo too as I found the pain I was feeling really hard to describe but after reading what the Dr s and ladies on here had to say I could tell them exactly how I felt which was really useful for both of us.
Hope that helps a little bit. always here if you want a chat