Dear..I dont think u r pregnant, from what I read, chance is so slim that u dont need to stress over it. Just relax.
If u r still worried, get a preg test, buy one that has 2 or more tests in one package, they normally cost around 10 bucks.
Is ur period irregular? If it normally is, then dont worry too much, stress can even make ur period later than usual!
Get a test done to be sure