ovulation day is generally day 13 of your cycle ( give or take ) which is the highest fertility date.. day one is the first day of your cycle. two weeks after your period makes you day 12...so your chances of pregnancy are at the highest. of course every woman is different in their ovulation cycle so protection is very important at all times..
You do not always have a 100% chance of getting pregnant. But 2 weeks after your period brings you very close to ovulation or to be actually ovulating. Even still, you may not get become pregnant just because your ovulating. There's always that chance. But never 100% :)
There is a very good chance of getting pregnant when having sex at any time, the odds go greatly up 2 weeks after your period. I assume you have talked with your boyfriend about what he will do when he gets you pregnant, like how he will pay his share of the costs of raising a child for the next 18 years??