Ying, whose name has been changed to protect her identity, did ask her boyfriend to use a condom but "he is a man, he did not listen.
"He used some once I was pregnant, but it was too late," said the softly-spoken girl, who moved into sheltered accommodation at Bangkok's Association for the Promotion of the Status of Women (APSW) when she was six months pregnant.
"My parents were afraid I would be embarrassed among my friends, so they told me to stay here," said Ying, from Pathum Thani province north of Bangkok. She now has no contact with the baby's father.
The adolescent birthrate has continued to rise for the last eight years, instead of the expected fall, according to Caspar Peek, country representative for the UN's Population Fund.
"Instead of going down, as you would expect to happen with higher levels of literacy, higher levels of development, money etc, the levels have actually gone up," he told AFP.
According to the United Nations, the birthrate among Thai teenagers was 47 per 1,000 girls from 2006 to 2010—roughly in line with neighbouring Cambodia, but higher than Malaysia's 14.
Thai health minister Pradit Sintavanarong said there were 130,000 births to teenage mothers in the country in 2012.
But he said the true figure of pregnancies among the under 20s is thought to be double that, with many girls opting for an abortion—a procedure that is illegal in Thailand under almost all circumstances.