It takes a good six months to know how your body will react to birth control pills. The first couple months, everything is kind of in flux because of the hormones. You should start to see a difference each month.

I've always started my pills the Sunday following my period, and then I don't usually have any bleeding until the placebo pills. If you didn't do that (you don't have to start that way, there are two different ways to start birth control pills), they might cause your body to react differently and make it seem like you're having a light period.

When did your "period" start? I'd wait until you start the second pack of pills before becoming concerned, myself.

When I started birth control the first time, the worst thing I had was morning sickness (and I was in high school. Concentrating on algebra while feeling like you're going to throw up is not fun).