Problem with Next/Previous page pagination after clickin on category or tag

This is the problem that I’m having

I am on this page:
https://www.website.com/?cat=4

When I click on “Next Page” in the end of the page i get this:
https://www.website.com/?cat=4?cat=4&paged=2
(404 page)

instead of getting this:
https://www.website.com/?cat=4&paged=2

I’ve been searching for a solution but I can’t find any, I don’t know what caused this in the first place.

Thanks