Could it have been in December

December sounds just about right. Usually it's nine months before your due date. Ask your doctor to be sure.

Most likely you conceived on or around December 29 or 30. However, a DNA test will need to be done to determine paternity.

Conception dates are give a take a week or two, so you can not pick a certain date. Even though the doctor, their dates are best guess ( very educated but still estimated)

After that, is there a reason to need to know ? If concern over who the father is, you will need a DNA test to verify