You do have to a ask for it… you have to request that they automatically attempt to renew an expiring rx. If you request for them to do so, they fax your doc a renewal request on the day your previous rx expires and your doc can either renew it, deny it, insist you come in for a visit first, whatever they want to do…
Any reasonable doc would just automatically renew an rx for test strips, or insulin or whatever, as long as you’re following up with them on a reasonable basis, but there are many cases where they wouldn’t just blindly refill prescriptions… eg antibiotics, short term narcotics, etc