Could I be pregnant now? Have been using withdrawal for 12yrs successfully.?

I have never used anything but withdrawal for bc, how likely is it that I'm pregnant now after 12yrs of successful bc? My AF isn't due until August 6th but I've had nausea for 3 days straight now wih no signs of illness and I had pink tinged mucus 4 days ago... I feel pregnant (have a 4yr old already) but it doesn't seem at all likey given the cirstances and its SO early, any thoughts/experiences?