I think I was injured by medical malpractice. I talked to a lawyer at church and she said that another doctor would have to testify against my doctor. Is that right?
Generally, yes. In fact, most cases require testimony from more than one expert medical witness. The expert(s) must testify (1) what level or type of care was necessary in the community given the medical issue; (b) that the appropriate level of care was not provided; and (c) that the inappropriate care caused the injury or death of the patient that would not have otherwise occurred.
This is a very complicated area of the lawyer, and I strongly suggest that you consult an experienced medical malpractice lawyer to evaluate your case.