I have developed a recurring sinusitis during the past 3 years. What is the best cure and prevention for it?

ENT evaluation. Many patients with "recurrent sinusitis" actually have untreated allergies or rhinitis. Alternatively, you may have chronic sinusitis (a lingering sinus infection which doesn't clear). Your ENT will be able to help determine what the problem is and treat you appropriately. Try a sinus rinse (using rinse bottle over neti-pot) daily as this helps minimize many sinus problems. Best wishes.
Treat reason for it. Recurrent sinusitis occurs for a reason. Underlying allergies or anatomic problems within the sinuses or nasal passages can contribute to recurrent infections. Best to see a primary care physician who can evaluate you and either make the diagnosis or refer you to a specialist for evaluation. Nasal irrigation can help in some cases (search healthtap for netipot).