Have you tried with a VERY minimal project?
If it still lags with that, have you tried uninstalling/reinstalling?
What else are you running in the background?
Are you up-to-date with virus checks?
Yes. The project that I'm running is very minimal. I also have my avast up-to-date and it's the paid version.
In the background I generally use nothing more than my photoshop and chrome. I know that it's not about my setup ( Intel core i7 3.40ghz, 8GB memory ram, GTX 760 2gb - more or less CUDA 980)
I didn't reinstall yet though. I'll try it.
Edit: The lag starts when I have no project loaded.