Do you run regular maintenance on your system? When I say this I mean running apps like Disk Clean or Ccleaner as well as something like Malwarebytes. Disk clean you can find in the control panel under admin tools and I'll include links to both Ccleaner and Malwarebytes below, both are free by the way. Another thing you could try is turning off your router for a minute or so. Sometimes my speed will drop and turning off the router, waiting a minute to turn it back on again usually works a treat.