What Causes Recurring Otitis Externa?

Hi :) Please help me. I had just finished my medicine against otitis externa (swimmer's ear) and then two days passed and then the pain came back. And I know it is otitis externa, because I know the symptoms very well, because this has happened very often. I donø' do anything with my ears, i don't rinse them often. So why is otitis externa coming back all the time? I always use some spray to put in my nose, that my doctor gave me, so otitis externa could stay away, but it doesn't work.