Just seen this post, Sherrardk and wanted to say how sorry I felt for you all.
As others have said, yes, you are perfectly entitled to ask for another Doctor to see your son at his next appointment.
Ask the nurse in charge of the Outpatient clinic if you can either see a particular Doctor if you knwo which one it is that you want to see or NOT to see a particular Doctor.
Be polite and explain what happened and that your boy was left in a lot of pain after his last visit and I am sure you will not have a problem.
If, by any chance, there is a problem and you are shown in to see the same Doctor who gave you the trouble last time, just say that you do not want this person treating your child, can you see someone else,please. Then keep repeating that until you see someone else.
Stay polite, don't lose it, just keep asking for what you want and do not enter into any discussion about it.
Hope all goes , if not well, then at least better next appointment.