Disabled parking tag

Other young vets - how do you get your pcp at the VA to sign off on a disabled parking tag? I've brought it up before and they always brush it off as "oh you just need physical therapy" or "if you keep thinking like that you'll never get better", basically saying I'm too young to necessitate this. Part of my push towards that is I go to the largest university in the country, that's a shit ton of walking on my part.

On my worst days I can't get out of bed, the pain is so bad in my legs and back I physically cannot move. On a good day I can walk but the pain immediately sets in once I stop regardless of distance, just the severity differs.

Also, I've done rounds of PT before and after a car accident I had the beginning of a bulging lumbar disc

Advice? I'm not SC for my legs/back but I do have an extensive history of treatment for it while in the service