Chances of being pregant using protection?

Okay, please don't judge me here. I'm sixteen, and had with my boyfriend on April 27 for the first time ever (both were virgins). We used protection. Then about two weeks later we had twice in one day and used a condom both times. I was put on birth control on May 2. My boyfriend said he only came/ed (not sure right phrase to use) a little bit the first time we ever did it. He said he didn't the last two times, and he checked the condoms with water afterwards, and said they didn't break. I just had a pelvic ultrasound done on Thursday, and nothing came up and I'm pretty sure even if I was pregnant, nothing would of showed up. I got a letter in the mail that the ultrasound came back normal. I also had bloodwork done but I have to wait to go back to the doctors for the results. I'm not sure. I've been stressing over school and family and friends so much for the past month and other problems. My period is about 2-4 days late. I'm so scared. What are the chances I am pregnant? I really am freaking out. I'm a good kid, good grades, working hard on everything, I just can't imagine what would happen. We were careful.