What Could Cause My Period Delay When I’m Not Sexually Active After Treatment For Dengue?

Hi, my period date was on 24 September but i Haven t got it till now on 3rd oct. I am not sexually active since last 3 months but i took emergency pill in june end and got regular periods after that for 3 times. I got dengue fever in August and was ill for two weeks.. what could be the possible reason for delay of my periods from the above?