If you are under 32 weeks its rare to even be asked for a note. Most companies will just take you. Check with your flight operator and see what their policies are. Most say that, if you can get insurance then you are covered. Insurance HAS to cover you. As legally they cannot discriminate against pregnancy in any way. Only after 36 weeks can they say that it is hazardous.
I went on holiday at 32 weeks and there were no problems.
The doctor will need to see your notes and see that you have not had any problems so far in the pregnancy. Then they may charge you and take up to a week to give you a 'safe to fly' note. I just got my consultant to sign my maternity book saying i was safe to fly, and that was with my baby also having heart problems. You only need one note. Not 2. If you ask your travel agent they will will able to find out the operators policies for you. They cant be seem to discrimate either though.
Hope that helps.