This isn't to defend bad doctors -- of which there are many -- or anything, but you are not a doctor, you don't possess medical expertise which even generalists have, and to be frank, your "lived experience," while not totally worthless, is more than likely not nearly as good an indicator for medical diagnoses as you seem to think it is. Much of the time, your recollection of what you lived is going to be incomplete, biased, or straight-up counterfactual (note that I didn't imply lying... you can be quite wrong without intending it) when compared against what actually occurred. That's why objective tests are used so often instead, something that most older patients, who recall more physical examinations and discussions, will often describe as a disconcerting shift in medical practices. To be certain, physicals are still conducted, but I'd suspect that, unless your doctor is quite a bit more seasoned, they're probably ordering more tests than you give them credit for.
So how about those tests?
Well, every test carries with it a false positive (and false negative) rate... I know of no non-trivial diagnostic test that is 100% accurate. Let's say that you test positive for some horrible disease, though. Naturally, you'd get a 2nd opinion (independent, likely different test). What's the chance that the 2nd test will produce a different result? Veritasium recently went over a pretty good explanation of exactly this scenario: if your initial test accurately diagnosed people as having a disease 99% of the time, you'd actually have only a ~9% chance of actually having the disease, given a positive initial test result, so a 2nd, independent test would likely suggest a different outcome. This doesn't mean that the initial test is worthless or bad; it just means that a test useful for screening diseases is still limited in what it can actually say. It also doesn't mean that a differing 2nd opinion is an indication of ineptitude of the first lab, though that is a possibility; again, it means that tests are limited in what they can actually say.
It certainly doesn't mean that you should disregard medical expertise for your own idea of what you think is going on. By all means, though, if that's the fire you want to play with, play with it to your heart's content. Just don't complain when you get burned.