Understanding my cramps?!!

I am a Hygienist in Washington State. I was working one day and I started having problems with cramping. Which is unusal for me. I never have cramps, I have lower back problems for one day when It is my time of the month.I had to leave work and go directly to Dr. Jackson's office. He took a urine sample and found out I was pregnant . Big surprise!! Dr said It was a shell from the fertilized egg that'd had lodged in the Fallopian tube. I had never heard of this before. Thank God for Dr. Jackson putting my mind at ease. We all got a laugh out of the situation . Thanks " Doc"