custom search module and pagination

[greek_batter]

Hello, recently I created a module for my personal needs. I have an issue with the pagination. I adapted my module to this guide http://nemops.com/creating-new-pages-in-prestashop/ and insted of GetProducts() function I created mine with a custom sql query which is based on data from the search form. 

 

Despite I make the initial 20 products to appear on the page when I press the second page of pagination the same products appear (if I store somewhere the query) or none appear (if I dont store the query).

 

How can I fix this? Is is possible the pagination to keep the first 20 products so in the second page only the 21st product and after to appear?