Medicare coverage for US citizens

Most hospitals and doctors accept Medicare

Yes there are Medicare providers.  There are some CVS stores but Walgreens is all over the island.  I do not know all of the CVS locations but I do know there is one in Fajardo.
If you switch to Walgreens, you can file your prescriptions in your home state and get the refills in Puerto Rico.  This will tide you over  until you hook up with a doctor in Puerto Rico.  Whichever you use, if you bring a prescription to a pharmacy in Puerto Rico, it has to be prescribed by a Puerto Rican doctor. 
To the horror of some expats but a blessing for others, there is a way of getting non-narcotic medications from pharmacies here, without a prescription, if you will pay cash.  So if you visit here and run out of your cholesterol medication, you will be able to purchase some pills without a prescription.

There is a Walgreen's on 3 right before you enter Fajardo.  It has been there for years.  Used to be the only thing in that area now there is a mall with a Walmart

Hi, Luquillo Bill. I had to laugh when I read the first part of your response, "There's a Walgreens on 3 ..." If you are on 3, you could be anywhere in Puerto Rico and  you eventually pass a Walgreens. 
I love this island.  BTW, I live in Humacao.

Before you enter Fajardo narrows it down

Yes, There are hospital and doctors who accepts Medicare.