Without an autopsy, you will have a very hard time proving the cause of death. Talk to your lawyer, ask if he regularly does malpractice. If he does not regularly do malpractice cases, find a lawyer who regularly does malpractice cases. This is not a job for your family lawyer, or divorce lawyer, or real estate lawyer. There a number of good malpractice lawyers in the Woodbridge area. You might want to use AVVO to find one.
Of course, you can always get a second opinion from another lawyer.