Hello, Would Like To Know Based On My Due Date,

Hello, would like to know based on my due date, 23/10/2016, when I may have concieved as unsure of father, had intercourse on the 26/1/2016, then with a different person on the 6/2/2016, started my lmp on around the 18/1/2016, but my period have been irregular, coming every 2 weeks, 3 or 4 weeks, please help, thankyou