Maybe I am missing something, but you will need to test within 10 days of your March visit.
Get the Rapid Antigen test and if you are no longer carrying the virus, then you will have your negative test. If your doctor is correct, then you should test negative.
And remember, you will need to be tested again here to board your flight back to the US. It is after all possible to become infected here, which is why the US wants a test within 72 hours of departure.
Any previous tests or doctor's notes really don't come in play. Both countries want you and your fellow passengers to be safe.