mobile

So i unlocked the bootloader and s off and all that and then i installed cm11 all is good n till the day after i noticed some sluggishness that increased with use then i returned to stock and had no sluggishness whatsoever the lollipop came out and my inner nerd was like install it or die the i installed cm12 and had the same issue as cm11 sluggishness then i wiped cache/dalvik cache which fixed it but it returned
So my questions are:
What is the cause of the sluggishness and can i fix it ?