Somewhat scared; Is this normal?

I'm a teen on birth controll and having sex. I was supposed to get my period on wendsday the 16th and after getting home from volleyball practice tuesday night I had brownish discharge in my underwear. I figured this was spotting and i put in a tampon and went to bed. the next morning i woke up with my period. I had a fairly normal period, using regular tampons and changing them about every 3-5 hours. On by sunday i wasn't using tampons any more and thought my period was over. Last night at practice i spotted a brownish discharge again.

Is all this normal?

....I was happy whenn I got my period cause i figured this ment i wasn't pregnant, but then i got scared when i started reading around on message boards and read that you can get a period while pregnant.