Mojave Issues...

Ever since I upgraded to Mojave, my essentially new 27 in. Macbook has been acting all kinds of wonky.

First off, it doesn't go to sleep mode, and instead, I'm forced to hit the power button every time to reboot/wake it up, and then proceeds to show me loading bars for a few minutes. Super annoying.

I'd be able to fix that issue, excepttttt System Preferences won't even open at all anymore (nor will Safari, or their new News app.)

Also noticing that my Mac as a whole is running way slower than before, with the good ole' spinning wheel making many more appearances than it used to when doing simple tasks like browsing.

Can someone help me figure out what the heck is going on here?