That you can actually notice... Well if you have been pregnant before it may take 20 to 30 days for you to "just know" that "something" is going on. However, the really annoying symptoms do not seem apparent until about the second month (50 to 60 days) but usually by that time you have noticed that your period is gone. If you mean morning sickness, that happens at around 8 to 12 weeks and sometimes it lasts until the four month.
Symptoms of pregnancy are very similar to PMS, so don't start buying baby things until you test and know for sure. It can be stressful when you're trying to conceive because just the mere fact that you "want to" get pregnant, can make you feel you "are" pregnant, but you're not.
Test at 14 to 16 days after sex, then test again every 2 days just to make sure. Good luck!