Wife got herpes but i don't have affair.

I know it's hard to believe. i am not a perfect husband but i am confident that i did not have any extramarital affair to anyone when my wife got infected with herpes. she was then few months after giving birth to our 2nd baby. Just by the look the female doctor gave me, she was blaming me for what happened without any words. i am still now seeking any advice because this thing always keep haunting me because i know that i did not touch any other woman except my wife that could cause her to get sick. i'm not asking for any sympathy from anyone. i just need some explanation if there is possible way that my wife may have contracted such decease. i know my wife well so she's out of the question. hope you give some enlightenment. tia.