A mum posted photos of her mysterious bruises in a heartbreaking final Facebook post before her death at 22.

The emotional post saw Sarah Armstrong, 22, warn others of the dangers of acute myeloid leukaemia.

The mum was diagnosed with the cancer after a visiting the doctors with "flu-like" symptoms and undergoing a simple blood test, reports Liverpool Echo.

She died on Sunday despite starting chemotheraphy.

Sarah had posted on Facebook: "So a few weeks ago I noticed bruising on my arms, legs, stomach, thighs and back but [I] thought nothing of it [and] I was probably just knocking myself on things and carried on with my normal day-to-day life.

The bruises began inexplicably appearing on the mother's body

"Then I started experiencing flu-like symptoms such as dizzyness, cold, hot flushes and tiredness.

"But [I] put this down to down to catching things at work because you catch all sorts working in a hospital.

"But it was one morning, I woke up with my arm aching and I checked my arm to discover I had a massive black/purple bruise that I couldn't possibly of knocked.

"Then that day I started experiencing my gums randomly bleeding for hours without it stopping.

"So on Tuesday [January] 21 I went to the doctors and was sent for blood tests.

Sarah Armstrong (left) was 'always laughing', say heartbroken friends

"The next day a new bruise developed on my arm, but this time with a lump, so I went straight to A&E, to which I was told it's not an emergency, go and get your blood done that your GP has sent for.

"The next day I got my bloods done and carried on with work and on the Friday, I was in work and had a phone call off a doctor to say my blood count is low, I have anemia and I need to go straight to hospital.

"To which I have now been told at the age of 22, I have acute myeloid leukemia, which is an aggressive blood cancer.

Acute myeloid leukaemia (AML) is a rapid and aggressive form of cancer that attacks the white blood cells.

It is a rare type of cancer, with about 2,600 new cases every year in the UK.

The NHS says acute leukaemia is classified according to the type of white blood cells affected - myeloid cells or lymphocytes.

Myeloid cells fight bacterial infections, defend the body against parasites and prevent the spread of tissue damage.

How does it develop?

AML occurs when stem cells in the bone marrow produce too many immature white blood cells, or blast cells, and usually requires immediate treatment.

Blast cells don't contain the same infection-fighting properties as healthy white blood cells, and too many can lead to a decrease in the number of red blood cells, which carry oxygen, and platelets, which help the blood to clot.

It remains unclear why this happens and, in most cases, there is no identifiable cause, the NHS says.

What are the symptoms?

Signs and symptoms of AML usually develop over a few weeks and become more severe as the disease progresses.

They can include pale skin, tiredness, breathlessness, frequent infections, and unusual and frequent bleeding (such as bleeding gums or nosebleeds).

People suffering from advanced cases can become extremely vulnerable to life-threatening infections or serious internal bleeding.

Anyone suffering from possible symptoms should see their GP immediately, the NHS says.

What are the risk factors?

If AML is suspected, blood tests will occur to check the blood cell production, and if the tests show a problem the next step is a referral to a haematologist for further tests or treatment.

Factors which can increase a person's risk include previous chemotherapy or radiation, exposure to high levels of radiation or the chemical benzene, and an underlying blood or genetic disorder.

The risk increases with age, as AML is most common in people over 65.

Chemotherapy is the main treatment, but in some cases radiotherapy is also needed in combination with a bone marrow or stem cell transplant.

Sarah leaves behind a two-year-old daughter and Jordan, her partner

"[I] have been in hospital since they told me on the Friday and expected to be here for a few weeks on chemotherapy.

"I still have a long way to go with more treatments and tests, however I am positive and I know I will beat this!

"Please anybody who has unexplained bruises, feels generally unwell [and] reads this goes [to] the doctors because knowing the symptoms can save your life."

The young woman went to the doctors with 'mysterious bruises' and 'flu-like' symptoms in January

The healthcare assistant, from Fazakerley, Liverpool, was described as a "strong and positive" woman.

Her childhood friend Danielle Johnson, 22, said: She was just full of life. I just can't believe it, we were sitting there laughing the night before she died.

"They started the chemotherapy and she was doing amazing. She was always positive."

"She was full of life. She was really positive, she did everything for everyone.

"She was always laughing and she always made everyone laugh. She was an amazing mum, she just always put everyone first."

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Sarah leaves behind a two-year-old daughter.

A GoFundMe page has been launched to raise money for Sarah's funeral.

The page reads: "We would really appreciate if people could donate anything you can afford,the funds will be going towards Sarah’s funeral costs,her baby girl and loving boyfriend Joel.

"Sarah wanted the images and story to be shared to raise awareness and hopefully help others catch this sooner."