If you are on Medicare, you DO NOT need a referral. You can go to any doctor that will accept Medicare. It is one of the nice things about Medicare. It lets us be our own advocate when our doctor doesn't know what to do with us or has no answer. You don't need a referal.
I'm in Canada, Addie. Things are much different here. We have Pharmacare which we all pay for (DH's company now pays for us). To go to a specialist the first time or for something new you need a referral. I have seen this doctor before, but it was for my vertigo and that was a couple of years ago. To see him for my throat and sinuses, I have to get another referral. My knee surgeon has stated that any time I have problems to call and make an appointment but it differs from specialist to specialist.