Afraid I might be pregnant..

When my ex-boyfriend and I were together we had unprotected sex several times. We broke up and he's with someone else now, but we've still been seeing each other on the side (yes, I'm aware this is not smart). I'm on birth control but I don't normally take it at a set time like is recommended for effectiveness. He always pulls out, but I know that's not always effective. With my birth control, my gynecologist allows me to skip the placebo pills and just continue the BC packs as long as I let myself have 3-4 periods a year. Typically when I decide to have one, I'll finish the pack and then not take anything during the four days I'm supposed to take the placebo pills. Usually it takes about 3-4 days for my period to start once I stop taking the BC. Well, the last one I had was in July, so I decided to have one this month. I was off my birth control for an entire week due to inability to get to the pharmacy and my period never came. It's never been late. I took a pregnancy test the second day it was late and it came back negative. That was a week and a half ago. I can't stop thinking I might be pregnant, however. I've been having weird cravings and I've been nauseous. But I'm not sure if it's just in my head or not. I plan on taking another test this weekend. I'm terrified. I'm a freshman in college, not even 19 yet, and no one in my family knows I'm still even talking to my ex. I love children, but I'm so scared. I have a great academic scholarship, full ride, but it requires me to live on campus all 4 years. Obviously I can't do that with a baby. Also, I don't have a job. I wasn't allowed to get one during my junior or senior years of high school due to the rules at the residential high school I attended, so I don't have any experience. My goal is to get a degree in Chemistry and go to pharmacy school to get my Pharm.D. I just don't know if I can do all that with a baby... Someone please give me advice. If I am pregnant, I'm keeping the baby. I just don't think I could give it up.