hello doctor,

i am 26 yrs old,i have 3 yrs old son, my last lmp was on july 17th.my usual periods will be within 36 days every time.but this time it leads to 52 days and i had self pregnancy check at home.it shows negative on my 45th day.i would like to mention that , in my first preganancy it shows me positive only after 60 days.

is there any chance of pregnancy if i had sex on my 26th day from my periods? tell me a solution? what i should do??/