Hi Catarina,

I hope you are well today and thank you for your questions.

suddenly wordpress is very slow

There can be various other reasons why your site is loading slow as described in the following pages.

https://www.bitcatcha.com/blog/2015/10-frustrating-reasons-why-your-website-speed-is-slow/

https://www.pickaweb.co.uk/kb/website-running-slow/

https://gtmetrix.com/why-is-my-page-slow.html

You can improve your site performance as described in the following pages.

http://www.wpbeginner.com/wordpress-performance-speed/

https://codex.wordpress.org/WordPress_Optimization/WordPress_Performance

https://wpengine.com/blog/page-speed-wordpress-performance/

https://themetrust.com/test-wordpress-site-performance/

To optimize images and load them faster, you can use any of the following plugins.

https://wordpress.org/plugins/ewww-image-optimizer/

https://wordpress.org/plugins/wp-smushit/

and when I click on preview pages, it redirects me to a weird link about credits and loans. Can you check what is it and tell me what to do if this happens again?

This seems to be the hacking or virus attack case so, please resolve it as described in the below pages.

https://wpbuffs.com/wordpress-website-hacked/

https://codex.wordpress.org/FAQ_My_site_was_hacked

https://www.wordfence.com/docs/how-to-clean-a-hacked-wordpress-site-using-wordfence/

https://sucuri.net/guides/how-to-clean-hacked-wordpress-a

https://askwpgirl.com/10-steps-remove-malware-wordpress-site/

https://wpfixit.com/remove-a-wordpress-infection/

Best regards,
Shufflehound team