She couldn't go to school, and she struggled to get out of bed due to crippling lower abdominal pain.

For more than three years, her symptoms were put down to acute period pain.

"I went to the GP when I was about 16, and they suggested I start taking the pill. But that didn't help," Mrs Sandford, now 37, said.

"From the age of around 17 I was referred to a specialist, and they tried lots of different pills.

"They tried a high-strength contraceptive pill, but that still didn't take away any of my symptoms.

"It was complicated, because about a year after I got my period, I was also struck down with IBS and Crohn's disease."

But eventually, the Charlestown woman was diagnosed with severe endometriosis.

Her doctor had been "shocked" by the extent of it.

"It was everywhere," she said. "It was all over my ovaries and all through my lower abdomen. I was only 18.

"At the time it was too widespread to be burned off. But what they did was put me on a heavy duty hormonal treatment.

"I think it was so hard to diagnose because they thought it was normal period pain, and because of my age, they probably didn't expect it to be something as widespread as that.

"It's a very sad thing, because it hindered my attempts to fall pregnant."

Endometriosis is a chronic condition which occurs when tissue similar to that normally found lining the uterus occurs in other parts of the body.

The tissue responds to hormones released by the ovaries, which can lead to bleeding, inflammation and scarring. There is no known cure.

Mrs Sandford said she had to have both of her fallopian tubes removed due to the damage caused by endometriosis.

"It had actually eaten away at my fallopian tubes, and left them badly damaged," she said.

"The extent of the damage all really came to light when I was wanting to fall pregnant."

It took six years, and nine full cycles of In Vitro Fertilisation (IVF), for Mrs Sandford to hit the "jackpot" and fall pregnant with her one-year-old daughter, Michaela.

"I sometimes catch myself looking at her and thinking, after all of the things that happened in that six years, and all the crap we have been through, it finally happened," Mrs Sandford said.

Mrs Sandford's story comes as a new Australian Institute of Health and Welfare (AIHW) report offers insights into the "painful and historically under-recognised condition".

Researchers at the University of Queensland used data from the Australian Longitudinal Study on Women's Health, along with health service data, to estimate the prevalence of endometriosis in two groups of women - those born between 1973-78, and those born in 1989-95.

The data showed one-in-nine women born between 1973 to 1978 had been diagnosed by the age of 40-44, and almost 7 per cent of women born in 1989-95 were diagnosed by the age of 25-29.

AIHW spokesperson Claire Sparke said the rise in earlier diagnoses for younger women likely reflected an increased awareness of endometriosis among the general public, and health professionals, leading to increased reporting and diagnosis.

"Women may experience pain, heavy menstrual bleeding, bleeding between periods, lethargy and reduced fertility, among other symptoms," Ms Sparke said.

As well as fertility, it could affect participation in work and school.

The report found there was an average of seven years between the onset of symptoms and diagnosis, and that there were around 34,000 endometriosis-related hospitalisations in Australia in 2016-17.

Mrs Sandford said she had lost count of the number of laparoscopies she has had to treat her endometriosis, although her condition was currently in "remission".

"Between being really unwell with endometriosis, and Crohn's, I missed a lot of high school.

At one point, my parents had to go and see my year adviser, because they were wondering why I was missing so much school. But I did my best. I didn't do very well in the HSC. But I pushed on and went to TAFE, and then to university, to become a teacher. It didn't stop me, it just slowed me down."

Mrs Sandford hoped she might inspire others to open up and talk about their condition.

"Share your stories about endometriosis, it's the only way to get the word out there and for our government to put more medical funding towards this debilitating illness," she said.