What Causes Shoulder Pain After Having Laparoscopic Salpingectomy?

Hi Doctor, I had laparoscopy-salpingectomy done on the 1 July 2011, almost 3 weeks ago, my left tube was removed. I am healing well, the bleeding has stopped and my stitches are closing up. Last night though, I had a pain on my left shoulder. I was wondering if I should worry or what? I had a miscarriage last year November, nothing was wrong with me, my HCG levels were very low at 10 weeks and it just took itself out, I had an evacuation done. I am generally healthy, no allergies, and have a 3 year old son. I am 24 years old, my height is 1.64 metres, last I checked my weight it was around 70 kg. Your advise would be trully appreciated. Thank you.