I know its a cliche. Finish your job and main first.
when you are just starting out myth is going to come slow at the beginning im afraid so keep at it. get an ilvl 55 weapon from your GC first if you can. it can take you places. do some ifrit hard or even garuda hard to get an idea other than the dungeons you been doing and start with your relic as well as following the other main story that unlocks after Garlean attack.

Its a lot to take but take your time. and welcome to end game