Are you saying that your girls have been sick this often because they're seeing different doctors each time? If so, that is not a reasonable assessment in my opinion.
I wonder why you don't insist on making your appointments with the same doctor. I'm guessing that you see different doctors because your appointments are same day appointments and you have to take the doctor on duty for those. Perhaps you can, however, ask to make a non-urgent appointment with one doctor and work to get one doctor as your primary care doctor.
I also suggest that your girls may be getting sick so often because of their environment at the moment. Who do they play with that are also sick? Are they getting enough rest, good nutrition, and a peaceful home? Does the family follow hand washing rules?
I know from experience that we often go thru spells of illness followed by spells of good health. I was ill so often one year that my employer sent me to their doctor for evaluation. I had my tonsils out and was immediately healthier. I suggest that your girls' immune systems are compromised by the repeated illnesses and it will take time for them to recover.
Do change clinics if you're not happy with this one but please don't blame the doctors for your girls illnesses. That is just not reasonable.
How could one doctor have made a difference?