That would be a social worker or case worker. This person would have experience deciding if you are disabled, gathering evidence such as medical records and filing the application. They would also know disability lawyers for the appeal stage in the event of denial, which 75% of all applicants experience.
Have a look at the 5-step sequential evaluation process used to determine eligibility. These aren't all hard and fast rules but will give you a general idea of what you're up against.
https://www.ssa.gov/OP_Home/cfr20/404/404-1520.htm