Are you usually quite regular with your periods? If so, then its possible you miscarried early. I had that happen to me last year. I am very regular and was late a few days. I took a test and it was a very faint positive. Two days later I started bleeding and had a normal period. The dr said that sometimes that's our body's way of getting rid of something that's not going well. does that make sense?
Or its possible something else is going on. Have you been on any birth control? Sometimes those b.c. methods - The depo shot, the IUD, can make your body act weird like that even after you first get off them.
You may just have to wait and see what happens over the next month. If you're still really concerned you could go into the dr and they can do lab work to check, or at least answer some more of your questions.
I see you want to go to college. This may also be an opportunity to "play it safe" from now on so you can finish school first. Trust me, I went through school with my kids while working full-time too and I would never recommend it - no matter how hard you try for it not to affect them, it does and its better to just get school done before starting a family, if at all possible.
Good luck with everything!