I’m very confused.
The professionals in whatever field you’re seeing will have a list of criteria which will help them to provide a diagnosis. This is a good thing as it aims to minimises human error and produce a standard. Without it, one doctor’s diagnosis of depression might be “highly likely to attempt suicide in the next 24 hours” and another’s may be “watched the first ten minutes of Up.”
I’m not a doctor but I’ve read relatives’ medical notes as a next of kin, and seen that they have score cards for many things. You’ll be reduced to a number for how responsive you are, how self-sufficient you are, and decisions such as whether you require continuous, hourly or daily checking are made on the back of this.
Now, your OP says, paraphrasing, “can someone mail me in private to tell me how to buck this system?” Your only options other than perseverance, as far as I can see, are either to pay for private treatment or lie about how bad your symptoms are. Do you want to lie, is that what you’re asking?
If you believe that their decision is incorrect then you might try contacting you local PALS to see if they can help, though if you’ve seen three different doctors and been rejected each time, you might struggle.
Some doctors are awesome, and some are dreadful. To an extent you’re reliant on luck of the draw. Someone I know fell down the stairs and dislocated her knee recently, after which it kept periodically dislocating (very painfully). the first doctor she saw said “go away and come back if it doesn’t get any better,” which it didn’t, and the second told her “you’re fat, have gastric surgery.” It took a third appointment to start the process of X-rays and diagnostics.