Pregnant while on the pill???Please read.?

I have been on the pill for almost 2 years. Last month I had a VERY VERY light period. Just mild spotting for a few days then on the final day it was heavier. Then it just stopped. This month I am already 2 days late. I have always been like clockwork on the pill. I am terrified because I don't want baby #4. Has anyone had this experience and been pregnant or not pregant? Thanks to all.