First, know that you're not alone. Second, Do NOT take this personally!! They most likely didn't fire you because of anything you did wrong. They fired you because they can't handle your case. That's not your fault, that's their shortcoming. And having you around is just a constant reminder of their failings. Of all the professionals out there, doctors are least likely to admit they can't do something. Which means the only ting left is blame the victim (i.e., patient).
Know that I'm so sorry you're going though this. But also know this isn't the end! This is a Golden Opportunity to find someone who genuinely cares. I've been able to do this myself, even though it took me a long time to figure this out (years). If you follow the steps below, you should be able to find a doctor who won't run away.(YMMV*).
"I thought being fired meant the doctor had decided there was no hope ..."
This is not "doctor shopping," this is doctor screening. Some doctors are in the point in their career that they want just the easy, routine cases. They are not likely going to want to help us. Younger doctors are often more willing to take on challenges to prove their skills. Older doctors, doctors close to retirement age, not so much... Unless they've specialized in tough cases (there are such doctors), but those doctors are rare.
IF YOU RUN OUT OF MEDICATION, you can go to your local Urgent Clinic or Walgreen's Clinic for refills until you ware able to get into your next appointment with your GP. Your GP will normally cover medications during a transition period. However, if it's your GP who fired you, that can really leave you in a sticky situation. In that case, call any specialists you see and let them know what's going on with your GP. They're also usually willing to cover temporary medication refills during a transition like this. You can also talk to your pharmacist. Many of them will be able to give you a few days' supply of vital medications, or medications you shouldn't come off quickly. Of course, narcotics cannot be obtained from anyone but a doctor. Worst case scenario, go to the ER.
Good luck, and I hope you find a doctor who will work for you.
*YMMV - Your Mileage May Vary