Did you do a bandwidth test from your computer?
Did you scan your computer for virus?
In order to solve the problem, you need to narrow down the
problem first to what causes it, was it your computer? Your
internet service provider? You modem/router?
You can narrow for example use another computer connect to your
internet to access, if the same slow speed, then likely to be your
network and not just your computer issue… if another computer is
fast, then at least u narrow down to your computer, then from there
you narrow down issit due to virus or networking configuration not
optimized or what…