There is no 24 hour 48 hour 72 hour ETC test to find out if your pregnant.
If you’re worried you will need to visit your doctor to be sure.
Sex stimulates the menstrual cycle as already stated.
Yes it is possible to get pregnant at any time with un protected sex.
(Even on your period/ or before it)
It’s a piece of rubber honey it takes 5 seconds with a skilled hand. Use it, it may save your life in the end, literary,