what does you back and chest workout look like?? Heavy dips/deads/chin/pullups/rows give alot of arm stimulation, you gotta find out weather your hitting them to hard or not hard enough for your genetics, If i am running splits and do a big back day, my arms are pumped and fried! Sometimes for the ego ill chuck in a hammer/db curl for around 2 sets.
What do your lifts look like also?? just looking at you weight to height i would say your fairly slim, maybe jumping on a fullbody would benefit you more??