Threatened miscarriage.

This is my 3rd pregnancy with no living children. I am 7 weeks today and have already been in the ER twice. Last time was a week ago. The baby measured fine and had a heartbeat of 106. The ultrasound tech said it was perfect but the doctor said it was low. My 1st real appointment is still 3weeks away and I am so scared. The office won't move it up, they say if it happens there is nothing they can do. They put me on progesterone. For the last 2days o have felt so sick. I have horrible lower back pain and think a possible uti. Part of me wants to go back to the ER and get checked again. I don't know what to do. I have had some bleeding that never made it to a pad. Just pink or brown once in a while when I wipe. I am so afraid my sweet baby is dead and just stuck in there. Has anybody had a low heartbeat and a little bleeding and had a healthy baby?