I couldn't believe it about the doctor either, surely a doctor should be able to feel a fully pregnant belly and figure out there is a baby in there!
I knew a girl at uni that put on a bit of weight over the year, one morning she woke up and was in so much pain she couldn't get out of bed. Her flatmates called an ambulance and sure enough she was in labour. Apparently she took the pill during the whole pregnancy and still had her period. I tend to think there was a bit of denial going on though