1. First - you have to understand that misdiagnosis does not always equivalent to malpractice, as some conditions are not easy to identify.
The best way to do is get your medical record to an unrelated doctor and review again. Then you will have a better idea.
If it is indeed malpractice, you should hire a lawyer instead. In most of the case, malpractice will mostly end up in a civil court for damage recovery.
2. Simple - each person is unique, which affects how the medication performs.
3. Yes and no. Some medication are by-product of petroleum. But many of them are not.