11 weeks and still haven't heard a heartbeat?

I've been to my OB 4-5 times already. She was always quick to point out my baby's heart but she still wont let me hear a heartbeat. Went today for my 11 week check up and she showed me a white dot flickering away but she didnt tell me how many beats per minute nor did I get to hear anything. With my first, I got to hear it right away. Is this normal?