Your definately not over training but mate you’ll most likely find you are genetically challenged in that department. Don’t stress, it sucks but there is nothing you can do about it. My back is much more developed than my chest and it shits me to tears but I deal with it.
Just train arms very hard and heavy with no more than two work outs per week on arms. Try cheat curls, cable curls, DB, ezy bar, preacher and like ST said lay off the iso exercises they do bugger all when you don’t have the muscle to isolate. Triceps will grow with close grip bench, dips, overhead cable and behind the neck press oh and cable push downs.
Large amounts of reps don’t do anything for me.
Tell me more about your cycle, structure, amount, duration etc.