Have Nasal Polyp, No History Of Sinus Infections Or Allergy. What Is The Cause ?

I recently found out I have a nasal polyp . I am very surprised as i show no allergy symptoms and have not had a sinus infection in more than 5 years. If i did have one i did not seek treatment cuz it was not causing me pain. I have not been sick in the last 5 years except i had cellulitis of my face. Antibiotics cleared it up. I eat extremely well raw veggies and fruits, salmon, nuts , whole wheat, etc. I thought that was why i don t get sick. I am a 40 yo female. 5 1 130 lb. normal BP, normal cholesterol. I take no medications. Dr gave me nasonex , used for ten days. i can breath a little better thru nose. my doctor thinks i should have the polyps removed but i feel i should find out why i got them in the first place or else they might just come back. what do you think i should do?