As a psychologist, my experience is that lots of physicians, even psychiatrists, want testing and a diagnosis from a psychologist before prescribing, so it might look like the psychologist is prescribing, when they are just diagnosing.
Incidentally, psychologist prescribing happens in some states also.
And all insurance plans do cover mental health per the ACA... It is one of the ten benefits that must be covered on all plans under the law.