Taking the train can turn into an ordeal for Nicole Lim. To others, she might look like a typical teenager, but she is battling several illnesses, including autoimmune hepatitis, which causes joint pain and fatigue.

"On several occasions, I have been asked to give up my seat," she said, adding that such incidents made her want to raise awareness of young people with chronic conditions who appear healthy.

With the help of three volunteers from Make-A-Wish Foundation Singapore, she put her thoughts and emotions into writing this year - something she did even while undergoing a liver transplant.

"Chronic illnesses can hit anyone at any age, and ailments are not always visible, even if people look perfectly fine on the outside," said Nicole, who shared her experiences in a book launched yesterday.

The event at Marina Bay Sands was also special as it was held together with celebrations for her birthday, as she turns 18 today.

Titled How To Be A Good Patient, her book, funded by BMW agent Performance Motors, details her journey discovering she had not one but three diseases at the age of 13, going through a liver transplant and finding out this year that she also has osteoporosis.

Using the pen name Y.K. Riley, she also captures a slice of her childhood in the book.

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"I was very active, climbing trees, bringing Fluffy (her late dog) to the playground, cycling. I didn't have to worry about getting dirty, but now I have to because I get easily bruised and infected," she said.

In 2013, she had gone to a clinic near her home in Punggol after having stomach pain and bloody stool, and after a friend pointed out that her eyes looked yellow. She was later found to have autoimmune hepatitis, an illness where the body's immune system attacks the liver cells.

She was also diagnosed with primary sclerosing cholangitis, a disease that causes scarring of the bile ducts in the liver, and ulcerative colitis, the inflammation of the colon.

Aside from medication to treat her conditions and manage symptoms, there is no cure. "It's like hitting the disease jackpot," said Nicole, who had to defer her polytechnic studies twice because of her illnesses.

At one point, she was told by her doctor that she had only five years to live before her liver would fail.

In May, she also discovered she had osteoporosis, where bones become brittle and break easily due to lower bone density. In August, she went through a successful liver transplant, with part of the liver from her mother, which she describes as a "second chance" to live.

"The doctors said it's like resetting the clock back to the time before I was in Secondary 1, and trying to maintain my liver condition with medicine," said Nicole, who will be studying law and management at Temasek Polytechnic next year.

Her parents work in the aviation industry and she has an older brother.

More than 200 copies of the book have been sold, and proceeds from the first print run will go to Save Our Street Dogs, a shelter where Nicole adopted her second dog Riley, as well as Make-A-Wish Singapore.

Her mother, Madam Camie Choo, 47, said: "We can't predict the future and it depends on how well the medicine works, but Nicole's illness has made her stronger."

To buy the book, which costs $34.90 (inclusive of GST), go to https://www.ykriley.com/shop