Steam games major lag vs origin & battle.net

[AT]

I have been encountering major lagging issues with most games within Steam.

After plugging in my external SSD the problem began, causing even Skyrim to drop to 6fps on the lowest settings suddenly. Meanwhile games within Origin run at 100fps and Call of Duty Cold War on Battle.net runs at 100fps+.

I've tried clearing the download cache, clearing browsing data and cookies and verifying game files but to no avail.

It seems as though something within Steam itself is causing these huge drops in fps.

Any advice or suggestions are appreciated!