Some helpful tips here from WPMU DEV. Watch out for plugin bloat though while installing some of these plugins. In theory there’s nothing wrong with having lots of plugins, but in practice that’s only true if all your plugins are top quality. 5 or 6 problematic ones could slow your site to a crawl but you can temporarily install P3 Profiler to check if you have any suspicions.
Despite being the world’s most popular blogging platform, WordPress still has its fair share of problems that are beyond irritating to deal with – especially if you can’t figure out what caused them in the first place.