Rocephin While Pregnant?

My doctor prescribed me one gram of rocephin yesterday. I am seven weeks pregnant. Reading about the medicine, it is a Category B. Meaning that it is not studied in humans, but in animals. It has had no proven harm on an unborn fetus. It should only be used as prescribed. Has anyone out there had complications because of this medicine?

I cannot take any other antibiotic.. and this was my only option. Someone please respond because I am so worried.

Yes. My doctor knows I am pregnant.