My site, which is small and only just recently launched, is pretty damn slow when it comes to doing admin stuff. What tools/techniques can I use to help narrow down whether the slowness is due to my host, theme (I'm using Divi), plugins, etc.?

For example, should I open up developer tools and see how long certain requests to the server are taking? If so, what should I look for and how should I interpret the results? Also, should I deactivate plugins one at a time and then perform the same action to see the result? Or does deactivating a plugin not completely eliminate the plugin as the source of the problem (i.e., do deactivated plugins still have some kind of footprint or effect on the site)?