Is it possible to get pregnant while on BCP??

My husband and I have been talking about ttc lately, but as of right now I'm still on the pill. AF is due in 4 days, yesterday I had a few drops of blood in the morning but nothing else, then this afternoon there was a very small amount of pink. My boobs and back have been killing me the last few days, and yesterday I couldn't even eat dinner I was so nauseous. I've been on the pill for 6 years and I've never experienced spotting like this, usually it comes a few days late. What do you think??