Bleeding at 13 weeks. Ultrasound and bloodwork were fine. Help?!?

Backstory: I have 2 minor tears behind the placenta which are supposedly "insignificant" according to the doctor. He put me on pelvic rest. I also have lyme disease and am on synthroid for my thyroid (had it removed in 99 from cancer). I went to the ER this morning after I noticed light pink bleeding in my underpants from the night before and when I wiped. No clotting, light pink, only minor occasional cramps. They did an ultrasound, the baby was moving and kicking like mad and the heart beat was 147. The doctor there said it was a "threatened miscarriage" and sentenced me to bedrest. I called my ob and he said he agrees and that the chance of survival are better then 50/50 and to call the office Tuesday for an appointment. Shouldn't they be more concerned? What's the real risk to my baby? Has this happened to anyone else and they had fine babies? Any insight would be helpful!