Honestly, it sounds to me like your build is off.
Can you post your stats?
Are you auto assigning points?
You should always be able to kill a mob 3* your level without restos and 4* your level with 1-2 restos. If you can't your build is off. Some choose to use combo's and some choose to use exp lix and beefier builds. Learning to dial in your build is a bit of an art. You might also consider that if your gear is that bad, that you either buy some plat, and sell some chests for gold (the lazy way), or go farm some mobs that are quick and easy to kill. Farm and then buy better gear.
You are level 120 so you should have meteoric armor.
For a rogue you should have a lux dagger (or dark aggy spear), and level 100 lux fire offhand axe from the carrows lux vendor. Wardens is obsolete at your level.
At level 120 you should start looking for a bossing clan. You wont progress through frozen/dragonlord/EDL without one. If you are an active bosser, any half decent clan should recognize that and gear you.
On my rogue I always used combo lixes to level. I liked them better than a rainbow. A rogue on a combo is a wonderful thing.
I suspect your issue is a lack of decent jewels/armor/weapons or a poor build.
As others said, do bounties, and dailies.