There’s a manhu I read like these whene the girl had one nigh with a guy then give birth...

http://www.mangago.me/read-manga/wangjuede_siyou_baobei/
Wangjuede Siyou Baobei

"A young girl wakes up in a hotel room and sees a man lying on top of her, but all she can remember is having a drink with her sister. Luckily she manages to escape from more terror, but still ends up pregnant. She passes out after giving birth, and when she wakes up her stepsister and stepmother can no longer be found in the hospital...
Five years later, she moves to Ningguo as an exchange med student, and with her is her 5 year old son who walks into another kid with identical appearance."

Yes yes it’s this one , thank you so much