Hello, I also have mental illnesses. Not everyone who has mental illness is disabled by it, in fact most people aren't. Also, disabled people are not helpless and it's kind of funny that you would say that because in order for you to have an ESA or SD your mental illness must be disabling.
If you only want an ESA, I would at the very least get a CGC on the dog before doing so. Just to restate, Emotional support animals are not allowed public access.
If you want a service dog, very few pet dogs are cut out to do the work and psychiatric service dogs must be very, very stable dogs and must do tasks as all service dogs must. My dog makes me feel good, most people's dogs do,but that is not a task and you can be fined for passing off a pet as a service dog.
You sound young, not that there is anything wrong with that, I'm one of the youngest members, but if you are minor, that will complicate things.
An "okay" dog is not an SD. Do you know were your dog is from? A shelter, rescue or a pet store? Or is you dog from a good responsible breeder who can talk to you about temperament? I's not that rescue dogs aren't great, but very few of them have the correct temperament to work in public.
Anyway, a service dog and a emotional support animal are not the same thing.