well you can always do the option of doing a fresh windows install.
this is the quickest and surest solution to know the baseline loading speed of your windows on your system. then youll know it has to be on your hardware specs/controller. drivers. next time it gets slow again. you'll know its a software service youve installed on your system.
you can try disabling all your services on startup and see if it makes a difference. press winkey+r. type "msconfig". services. hide all ms servcies. disable all. also go to startup. and disable all of them if you want.
first check if this improves your windows loading. and if it does. you do the same procedure and enable a service at a time per manufacturer.