The key to winning SSD cases are the medical records and what restrictions your doctor has imposed. You need to see your doctor so that any new problems are properly documented.
DISCLAIMER: David J. McCormick is licensed to practice law in the State of Wisconsin and this answer is being provided for informational purposes only because the laws of your jurisdiction may differ. This answer based on general legal principles and is not intended for the purpose of providing specific legal advice or opinions. Under no circumstances does this answer constitute the establishment of an attorney-client relationship.
You don't have to be under the care of a doctor, but having medical evidence is critical to proving your case. SSA may send you to a doctor for an "independent" medical or psychological exam, but relying on that for a thorough and fair assessment of your conditions and limitations is risky. Further, many adjudicators, including judges, will question how disabled an individual could possibly be if he or she is not receiving regular treatment.
If you are currently receiving Social Security Benefits and are undergoing a "Continuing Disability Review", Social Security is reviewing you to determine whether there has been a medical improvement that would allow you to return to work. Medical treatment and the documentation that would generate is useful in showing your medical status. If you are not receiving treatment, Social Security may send you out for an evaluation to determine your current medical condition.