Possible ectopic pregnancy

I had an ectopic pregnancy before, I am now positive in pregnancy test with 6 weeks and 5 days ongoing but the ultrasound doesn't detect an embryo on my uterus, I returned to the ob and only suspected of miscarriage. I have pain on my lower abdomen that doesn't go away and a brown discharge occasionally that started on friday night. My vitals are ok but I'm still worried. The doctor said to wait for another 2 weeks for another ultrasound. Do I need to get another opinion or just follow the doctor's order.