Seriously, I am new to the game and want all of the mythos packs. How often do they reprint?

At it has been stated on all the other numerous threads about "reprints" (like this: https://community.fantasyflightgames.com/topic/308863-newer-player-carcosa-pack-reprints/ ) nobody knows.

It could easily take from 6 months to a year (maybe less if you're lucky), but sooner or later you'll have them all.

Right now there are many campaigns to keep you busy for a while.