Due dates are calculated according to the last menstruation date and this formula:
Due date = last menstruation - 3 months 7days
From the formula, it appears that your last menstruation was probably on the 17th November.
(Last menstruation = due date 3 month – 7 days = 24th August 3 months -7days=17th November)
If your last menstruation was on the 17th of November and your cycle lasts 28 days then you probably conceived at the end of November or the beginning of December.
Because you slept with 2 men in a short period of time (within a few days of one another), both men have chances of being the father. DNA-testing is the only way to identify the real father.