Oh its better than that.
The medical condition exemption is due to the ADA (Americans with Disabilities Act).
Under that law not only must they let you enter, they are not permitted to ask you what your medical condition is as that's a violation of your privacy.
And if they refuse you entry, you can sue them.
And they know that.
However… be warned that you will not be well received by the other shoppers. That may not seem like a big deal, but if they're your friends and neighbors, its might be.