While birth control CAN and often does cause lighter, less troublesome periods for users, that isn't the case for everyone. (I was on a prescription about a year ago that made my cramps worse than normal, despite the fact that for many birth control prescriptions will make cramps lessen for users)
Everyone reacts somewhat differently to hormonal birth control, and each different prescription can cause different effects in your body.
I'm assuming that this period was how your body reacted to the drop in hormones after the first month. (When you're on birth control, you don't have a real period, but instead a withdrawl bleed. The withdrawl bleed is triggered by the drop in hormones when you're on the placebo week of your pills)
My suggestion is that you see how this next month goes; if your withdrawl bleed is the same as the one you just had, or is still at a level that is worse for you (even if it's not quite as bad), you should go to your gynecologist or whoever prescribed you the pills and talk about trying out a different prescription, in case it's just an effect attached to this particular prescription of pills.