His stomach was bloated and his stools were loose and dark.
At just 26 years old, he found out that he had stage three cancer of the colon.
Kiat (not his real name) is among the youngest to be affected with the disease, which normally affects those past the age of 50.
Colorectal cancer runs in his family, and his father and aunt had developed the same condition before.
For Kiat, a Singapore permanent resident, it started when he developed stomach cramps two years ago.
Said the IT consultant, now 28: "I didn't think it was anything. I mean, many people get abdominal pain."
But then, he started losing weight, going from 60kg to 53kg in just a few months.
The regular blood donor of six years was also surprised when he was turned away from donating blood.
He said: "I was told I had low blood pressure. I had also been feeling faint several times a month."
Then, in December 2010 when Kiat was in Malaysia, the bus he was on made a sudden turn, and he felt a sharp pain.
He said: "It was like I was being stabbed with a knife, like something tore inside me."
He bore with the pain for the rest of the trip, but when he returned to Singapore a few days later, he developed a fever.
Feeling weak and unsure if he could get help by himself, he called for an ambulance to take him to hospital.
Initially thinking that Kiat was suffering from appendicitis, the doctors scheduled for him to undergo surgery to remove his appendix.
But during the operation, they noticed a hole in his colon.
It was then that they found out that he had colon cancer.
The cancer, caused by a hereditary gene leading to a condition called lynch syndrome, had spread to the lymph nodes in his abdomen.
Kiat said: "The cancer had literally eaten a hole in my colon. I was shocked. "I kept thinking that I was so young. I don't smoke or drink - why was this happening to me?"
His wife, 29, a Singapore PR who also works in the IT sector, said: "He kept asking the doctors how long he had left. He couldn't eat and kept crying.
"I was so scared of losing him. I prayed every day for him to get better."
The couple do not have children. To prevent Kiat's cancer from spreading, doctors removed the lower half of his colon. They also started him on chemotherapy to kill any cancer cells that remained.
For the next eight months, Kiat had the chemo drugs injected into him every three weeks. He said: "I felt physically weak after the sessions. But I kept telling myself that I had to be optimistic, be positive."
To take his mind off the cancer, Kiat continued working whenever he could. He also continued to travel and hang out with his friends watching soccer and playing PlayStation games. The cancer is now in remission.
He was given the all-clear in the middle of last year and is no longer on medication.
Looking back, Kiat is thankful to his wife and family, who supported him throughout my treatment.
He said: "There were days when I was down or had a short temper. But they were always patient and gave me space.
"I want to tell other young people that colon cancer is no laughing matter...If you have any of the symptoms, it's best to see a doctor right away.
"And if you know of someone with such a condition, please try to be understanding and supportive."