Hello, and I hope i can help you today. I believe there are three possibilities in this scenario. First, if you never had a follow up beta HCG value after you went to the hospital, there was no way to know if you just had an early pregnancy (with implantation bleeding) or a miscarriage. So you may just still be pregnant, and never miscarried at all. The second possibility is that, if you have been having unprotected sex since the miscarriage , that you conceived a second time and have a new pregnancy. Thirdly, pain on one side can sometimes be a symptom of an ectopic or tubal pregnancy, which is when the pregnancy implants outside the uterus. Nothing can be seen in the uterus on ultrasound, and if it is too early, there may not be any findings near the tube that may be recognized on ultrasound. For that main reason, as tubal pregnancies, can cause severe internal bleeding and even death if emergency surgery is not performed, I strongly recommend you go back to the emergency room or see a doctor to obtain a repeat beta HCG valua and an ultrasound. If things are not clear at the time, repeating another hormone level and ultrasound in 48-72 hours is recommended. If you find your pain on the left side gets worse, or is associated with feeling nausea, if the pain moves to your bellybutton area or radiated to your right shoulder, or if you feel dizzy, have fast heartbeat, or weak, please go to an emergency room promptly. I hope I was able to adequately answer your question today and that my advice was helpful. Best wishes, Dr. Brown