Sorry to hear that you got fired. Did your employer, and past employers, explain why you were fired? If it's a common pattern then perhaps you could work on whatever the issues are.

If you are not able to keep a job due to mental health issues, consider applying for disability. There is no shame in accepting the help if you truly need it. Disability has definitely helped me, and now I am working part-time while receiving disability. It is possible to do both eventually - be gentle with yourself.