I would certainly call your physician and discuss this with him/her, since it is spreading and you are having other bothersome symptoms as well, there is definitely some cause that has not been identified.
I would say that "yes" you should have more blood tests, and any other the specialist recommends.
You have a problem that should be resolved by a physician.
The prednisone/hydrocortisone protocol is a standard approach to the kind of symptoms you have demonstrated. They haven't done anything that could be considered malpractice.
If there is no resolution, go back to your physician. They will decide what tests to perform. Most likely this will include bloods. There are hundreds of different kind of blood tests. Most likely you will be referred to another specialist.