I don’t know if I am or not, but if I am…Advice?

Okay, I don’t even know how to begin this, really. There’s a lot to say about the whole thing.
I guess I should say that I’m not even really sure if I am pregnant or not, but as each day goes by I’m more and more positive that I am. I took two pregnancy tests before, but the answers were both different. I’ve been going through the symptons too. However, it’s only been a month since I last had sex and my period is only off by a week-ish. So I don’t know.
But again, I’m really afraid that I am.
I’m 17 and I’m in college. I have, and I’m not saying this to be arrogant but to simply stress the point, the brightest future of anyone I know. I graduated high school early as one of the top five students in my class. I’m graduating university early and I have solid A’s in all my classes. I’m in a great university, from which I’ll get a dual degree (accredited by both the US and the UK) for a double major in International Relations and Economics.
And I think I’m pregnant.
Now, I guess I should mention that I had an abortion when I was 11, and I don’t regret it a bit. But that was because I was raped and simply too young. And besides the people who helped me get the abortion, I never told a single person about it besides my fiance.
But I can’t get an abortion this time, I couldn’t live with myself. As much as I don’t want to have a child yet, I can’t. My fiance and I are both against it personally, though we’re pro-choice politically. I know he won’t leave me or anything like that, though he isn’t anymore thrilled at being a parent yet than I am.
But I can’t be pregnant right now. I just keep thinking about how unfair it is, even though I know it’s irrational. We were so careful, I never left around, I was just planning on getting an IUD this week. I guess I’m just scared and don’t know what to do.