I thought your most fertile time was 12-14 days BEFORE your period not after it as ovulation does not generally occur until 14 days after you finish bleeding. The pill isn't your true period though, the bleeding you get from a pill is just withdrawl bleeding from the hormes you've been puttin into yourself, it's not your 'true' cycle. I am on the same pill (Yasmin) and from what i understand it inhibits the release of an egg. I think you are possibly at risk of becoming pregnant but not a high one. it'll depend how the pill cycle sits on your true cycle if that makes sense. Go see your GP again just to be on the safe side.
I'm totally parianoid about having an unwanted pregnancy so I'm on the pill and always use a condom, I would suggest this as the best course of action because then if you do forget a pill or be sick or something, you still don't have to worry.