Confused plz help

Hi I'm all new to this, need some help and advice.

ive been on the Yasmin pill for 9years and just been on holiday any way I took my pill back to back or was suppose to but I came off the second pill packet mid way so I stopped it on the Friday of the second week, I had intercourse twice after that and 6days later I have a withdrawal bleed. I'm on day the 6th day of the bleed and have been getting stomach cramps and a pain on the left side of my back I feel nausea but my breast are not tender. 

Is this because I've stopped my pill after 9years or could it be a sign I may be pregnant? I have decided to try for a baby so the intercourse was unprotected.

thank you in advance for any advice..