I thankfully don't have personal experience, but I have friends who have had this and my father-in-law is a dermatologist (although that doesn't make me any more knowledgeable).
I'm afraid your pharmacist is right, and it does take a long time to get rid of it completely. Whatever treatment is prescribed to you, you have to take completely, even if you think you don't need it anymore, because if you don't the risk of recurrence is much higher.
It can be months (or more.....) before you get rid of it.
I can't think of how Vicks or oil would have any effect on this, sorry...