Whats going on with me?

Since about Friday I do believe I have having light brown mucusy discharge with NO odor. Today in the middle of the day I noticed I had a big brown spot in my panties.. No its not number two. It has a little tint of red in it WITH NO ODOR. My mom says its spotting. But I have NEVER spotted before starting.

I started the Depo shot when I was 15 (17 now) I stopped taking it Dec. of last year (2008) And in June of this year(20090 I was put on the Birth control pill low dose. Could this be a sign of my body coming off the depo shot? Because I have a whole week before my none active pills for birth control.

My boy friend and I had unprotected sex the beginning of the last week of Sept. When I was getting ready to start- I know stupid but he was being put in prision- I felt a little sick like 3 weeks after but then it went away. I took a test just to be sure it said negitive. But since I had been on the depo shot people are telling me that I could be prego and not know it.

Has this ever happend to any of you?