A group of women are calling on the NHS to give doctors better training on endometriosis.
The condition affects 1.5 million women in the UK and takes an average 8 years to diagnose.
What is endometriosis?
Endometriosis occurs when tissue that behaves like the lining of the womb is found in other parts of the body.
This lining can start to cover the ovaries, fallopian tubes, parts of the stomach and bladder or bowel.
The condition can also affect fertility.
Endometriosis mainly affects girls and women of childbearing age. It is less common in women who've been through the menopause.
What are the symptoms?
Symptoms include chronic pelvic pain, extremely painful periods that stop women taking part in normal activities, pain during or after sex and painful bowel movements.
Pain or discomfort going to the toilet, bleeding from your bottom or blood in your poo are also common - as is excessive tiredness.
What are the causes?
The cause of endometriosis is unknown.
Several theories have been suggested, including:
genetics – the condition tends to run in families, and affects people of certain ethnic groups more than others
retrograde menstruation – when some of the womb lining flows up through the fallopian tubes and embeds itself on the organs of the pelvis, rather than leaving the body as a period
a problem with the immune system (the body's natural defence against illness and infection)
endometrium cells spreading through the body in the bloodstream or lymphatic system (a series of tubes and glands that form part of the immune system)
Are there any treatments?
There is currently no cure for endometriosis, but there are treatments that can help ease the symptoms.
anti-inflammatory painkillers – such as ibuprofen
hormone medicines and contraceptives – including the combined pill, the contraceptive patch, an intrauterine system (IUS), and medicines called gonadotrophin-releasing hormone (GnRH) analogues
surgery to cut away patches of endometriosis tissue
an operation to remove part or all of the organs affected by endometriosis – such as surgery to remove the womb (hysterectomy)
Do treatments cause any other problems?
One of the main complications of endometriosis is difficulty getting pregnant, or not being able to get pregnant at all.
Surgery to remove endometriosis tissue can help improve fertility, although there is no guarantee that women with the condition will be able to get pregnant after treatment.
Surgery for endometriosis can also sometimes cause further problems, such as infections, bleeding, or damage to affected organs. If surgery is recommended for you, talk to your surgeon about the possible risks.
Read more about the complications of endometriosis here.
What is the guidance given to doctors to speed up diagnosis?
The All Parliamentary Group on Women's Health said 40% of more than 2,600 women who gave evidence to it reported they had seen a doctor 10 times before being diagnosed.
In the guidance, doctors are told to consider endometriosis in women reporting even just one symptom, such as pelvic pain or very painful periods.
It also suggests a number of ways of helping to diagnose the condition, such as ultrasound and keyhole surgery to look inside the body (laparoscopy).
The guidance warns that the possibility of endometriosis should not be excluded even if abdominal or pelvic examinations or ultrasound or MRI are normal.
GPs should also consider a three-month course of painkillers such as paracetamol or ibuprofen for pain and can advise women on taking the Pill to help relieve symptoms.