It is or might be a 'Short Code'. You can do an Internet search for short code lookup to find a site that will look it up . I did and it is a CVS Pharmacy short code.
That's sounds odd you are getting a message without knowing where it is from, Confused0581. Let me help you with your messaging concern. Did you try contacting Athena Health to verify if the message was from them? Do you went to block the number from sending you a text message? Please share more details so we can assist you further.