If its the exact same thing as me then your only real option is to backup your data, format the HDD and reinstall High Sierra. I also suggest NOT installing the new APFS+ file system until its been worked on a bit more, it isn't even compatible with Time Machine for pete's sake!
-Spinning beachball cursor every several seconds and after every action
-iTunes music suddenly stops playing, resumes, then stops again
-Entire system stops responding except for the cursor for upwards of 10 seconds repeatedly
-Boot times become idiotically long (5-10 minutes or more!)