doctor problems

Im alittle worried? So i saw my specialist almost two and a half weeks ago, he was worried because one baby was bigger that the other so he didnt want to wait for me to be seen until two weeks later how ever his office was going to be closed for a week. So he sent me to a maternal fetal specialist the following week to be looked at and told me to call that friday after i saw her to make an appointment at his office. She saw the babies said they are ok one is smaller but he is growing but she wanted me to be seen once a week by my specialist. So that friday i called to make an appointment to see him again but the receptionist simply said they would call me back to give me an appointment. The weekend went by when i hit tuesday w out a call i called them again and she said she was backed up and they would call me its almost thursday and i havnt been seen this week. Should i be worried? What can i do about this? I feel like if i called i will be told the same thing again. By the way im 21 weeks 4 days pregnant with modi twins last ultrasound one baby was 9oz and the other was 14oz.