Could I be having an ectopic pregnancy?

I started a new birth control that is progestogen only. I am currently half way through my third pack of this particular kind of pill. Anyway, they told me when I started taking them that I probably wouldn't have a period that comes the same time every month. I however have not had a period now in 6 weeks or so. I have took two test at the beginning and end of last week and both came back negative. This morning however, I woke up with pretty sever pain in my lower abdomen. Movement made the pain worse. It was a very painful "cramping" type pain. I thought I maybe just need to use the restroom, which was extremely difficult, but it didn't seem to give me much relief. As the day has gone on the severity of the pain has gone down, but movement still makes my lower abdomen hurt. Any help/advice would be much appreciated.