I've been in and out of hospitals all my life because of cystic fibrosis.... mistakes get made. Usually when a doctor doesn't read your notes and walks in "blind" and treats you. I've been prescribed antibiotics that my records clearly show not to give. 4 years ago I was prescribed an antibiotic in an emergency room for pneumonia by a doctor who didn't look at my notes and had no clue I'd had a double lung transplant. Once I had asked if he had checked with my transplant doctors if this drug was ok, he immediately went and read my notes. Antibiotics have different effects on transplant meds and their effectiveness. Drug interactions can be dangerous, and when a doctor doesn't bother looking at your notes there is plenty of room for bad things to happen that shouldn't.
Having said that, 99% of the doctors I have seen are good at their jobs. It's not an easy job. So for medical advice, that's where I go. And I have refused to take some drugs prescribed, if the side effects are just too risky and out weigh the benefits. Doctors sometimes don't even know them, and or never mention side effects.
For diet and exercise advice, I've spent years researching it and experimenting with it. And asking questions. As that post states, taking control of your health relies a lot on yourself. You usually know when something isn't right, or when you are onto to something.