Change URL data on page load

Hello I have a small website where data is passed between pages over URL. My question is can someone break into it and make it pass the same data always?

For example let say, when you click button one, page below is loaded.

example.com?clicked=5

Then at that page I take value 5 and get some more data from user through a form. Then pass all the data to a third page. In this page data is entered to a database. While I observe collected data I saw some unusual combinations of records. How can I verify this?