Ditto advice to call your DoDMERB assigned contact and discuss with them. Do not start the treatment until you know it’s okay and how to handle with regard to your appointment and reporting in. This close, you will probably also want to discuss with Admissions. Read up on the medication’s side effects and requirements, as you should for any medication going forward as an adult.
This is the accession standard, see page 40.
On I-Day, your primary care provider becomes TRICARE Prime, the military health insurance network. After Plebe Summer, you will have access to specialists such as dermatologists, if needed, and Rx will be prescribed if indicated. You will learn how to seek and schedule care.
It’s fine to remain on your parent’s insurance, as a fallback, in case you leave USNA in the next few years, but TRICARE will be your primary and specialist care provider.
Presumably, this is not life-threatening, so you can get through PS and take as good care of your skin as you can. Once the academic year starts, you can follow up within the Navy system. There are thousands of mids who came before you and likely quite a few there now who are seeing a Navy derm doc.