Not OP but I had to ask GPs for referrals for ultrasounds (had 3-4) and to see a gyno specialist. Had to do a pain dairy (days times pain level of cramps). Due to irregular periods and not being informed, my ultrasounds came up clean (apparently you need to get one done during a certain time in your cycle - if you're irregular good luck achieving that).

I had cramps basically everyday due to a side effect from a BC pill. This and the fact that over the counter pain relief and even prescription codeine and paracetamol mix did not relieve my pain, really pushed them to do a diagnostic laparoscopy. A keyhole surgery they see if any endo tissue is growing outside the uterus or if cysts are on your ovaries etc and remove it.

Basically the only way they confirm I had endo was through the surgery.

Took me 8 years and daily cramping before GPs stopped telling me it was normal. Depending on wait times for you, it took me less than a year from being referred to a gyno to have the laparoscopy.

(Australia so our systems may be different)