My ex wife is an RN at a local hospital. I know she has accessed my records as she has told me all medications I am currently taking. She is attempting to use this as a means to keep me from seeing my son.

So report her to the admin and HR department at the place she works.

Not sure why she would do this, all she has to do is go to court and they can order you to provide the records. So if there is something you are taking that would effect you visits, then she can get that information legally

This is two issues.
1. one custody, has she filed in court to change custody due to this, if so hire an attorney to show that the medication does not effect visit.

2. her access records, report to the place she works