What Causes Delayed Periods With Cramps After A Breast Surgery For Lump?

Recently I had surgery to get a lump removed from my breast and around that time I was supposed to get my period, but did not. Now it's been about 9 days since the surgery (also had general anesthesia) and still no period. I did feel some cramps last week and a few times in the last few days. Should I be running to the drug store for a pregnancy test? I am pretty nervous.