You don't always have symptoms when you are first pregnant, but if you get morning sickness you'll know it. You can have it without actually throwing up btw, but you would probably feel nausea and other symptoms (It's no substitute for a real test, but the free online pregnancy test at http://www.geocities.com/Materni_Tee/test
gives you an idea of some other early symptoms). If you think you are pregnant and are worried about it, a proper test is probably the best course of action to take. Good luck!