Small period, is this a miscarriage?

Dr. told me i was positive at 5 weeks. Next day started bleeding brown and red blood. Only a few tissue like clots ped. 91 hcg dropped to 51 hcg. Took pg test today and is still positive (it's been 5 days since the 51 hcg results) Other than a little dizziness, little tenderness & slight twinge pain in pelvic area...no other symptoms. Basically feel like I'm having a period. Dr. told me to come back in a few days for followup. Is this a miscarriage? Is there any chance I could still be pregnant?