Barb seems like damage is weak?

Not sure if I’m doin something wrong. I got like 15 into my weapon mastery seems like on nightmare I can barely take down weak enemies…I think I’m level 45? Idk.

Sounds like it’s time to gear up again. If you don’t know/remember what rune words are yet you should Google them. Malice (Mace) works until you find better runes. Also, using a debuff/buff shout in your strategy is important if you’re not already.

your barb is hardly weak.
maybe its your skill / stat distribution.

my guess is your gear is crap, particularly your weapon. just taking into consideration that barbs are extremely gear dependent.

do what the dude above said - make some runeword gear, maybe do nightmare countess runs.

edit:
maybe you could do some normal Diablo / Baal runs for some sets / uniques to help.
or even nightmare andy if you got her available.

like i said, they’re extremely gear dependent.

Imo you shouldn’t be speccing into any weapon masteries until you have your end game gear, then you can use a respec. Those skill points are better used elsewhere early on.

Nope my barb is lvl 88 ssf already has full ik and can solo everything on hell difficulty.

You need to upgrade your weapons. Look to make black flails (thul io nef).