What Windows version do you have? 7 8 10? And what bit? 32 or 64?
What is the rest of your hardware - CPU, HDD(s) and / or SSD(s).
What is your antivirus / antimalware? It is possible to configure this too aggressively so that it is continuously scanning far too much. If you have HDDs that can really kill your PC's response (we saw that at work where machines were effectively unusable for 20 minutes after booting up due to a startup scan running on HDDs)
When you see the slowdown, what does task manager show is hogging CPU and RAM?
Windows is normally on a C rather than D drive (that may be a typo?). But if one drive isn't working well on your PC, in some way the files are on the verge of corruption, or the drive itself is dying, that may affect response of PC if it is trying to read / write to the drive?