All women are different but usually 3 weeks.

It takes more than 3 days for an embryo to implant. Although some women experience a sort of cramping/pinching/tugging sensation following implantation (I have, both times), most will only notice it if they are paying VERY close attention, and even then some women will feel literally nothing. Most very early pregnancy symptoms are caused by elevated progesterone, so it can be nearly impossible to distinguish from normal PMS symptoms.

A missed period isn't always the most reliable indicator of pregnancy, either, since spotting/bleeding in early pregnancy is not uncommon. I started getting faint positives 5 days after my IVF transfer so I knew I was pregnant well before an expected missed period, but I also had spotting/red bleeding starting 7 days after the transfer. If I hadn't 100% known for sure I was pregnant, I might have mistaken it for lighter than normal period.

Three days after you have sex (assuming an egg was fertilized then), you wouldn't even BE pregnant yet! After an egg is fertilized, it's going to take up to 10 days before it implants into the lining of the uterus and establishes a pregnancy. Until that happens, a woman isn't pregnant. Therefore, it would be impossible for her to feel "pregnancy symptoms" three days after having sex.

A woman's FIRST "symptom" of a suspected pregnancy is always going to be if she misses her period. Before then, any "symptoms" are figments of her imagination, or else they're being caused by something other than pregnancy.

Too soon for symptoms..

You have gas. Take Beano. You are not pregnant by 3 days.

that is from sex

It takes about 10 days for egg to get to your womb and then implant there so after a late period and a positive result nausea starts from around 6 weeks pregnant, cramps show period about to start.

Of course it's too soon. Basic common sense.