It sucks to get sick or just not feel well when you are vacationing in Las Vegas (or anywhere, really). One of the benefits of the recent proliferation of CVS and Walgreens stores on the Strip is that some of them also have basic medical services. CVS has Minute Clinics at the locations near Bally’s and Park MGM. The Walgreens near the Venetian also has a Healthcare Clinic.
Services at these clinics are limited and tend to focus on colds and minor injuries, but they do have prescribing authority if you need a prescription. They take most insurance plans and seem to have reasonable rates if you don’t have insurance.