What Are The Side Effects Of Lo-estrin24 Birth Control Pills?

I have been on Lo-estrin24 Birth Control since January 2010. I won't lie, the last few months I have been a little dogdy with taking it, but I've always taken my pill within a two hour radius of 12 pm. I've been under a lot of stress with school and have been eating poorly (some days excessively and most days not enough). Today I am at the end of the second week in my BC pack and I just got a full on heavy period. What causes this? Should I be concerned? Should I go see a doctor?