6' 1" 190 lbs, yet I have 12 inch arms.

I've been lifting for the past 2 years, and have gained a total of 45 lbs. I have seen large gains in most lifts I do, arms included. However, there has been no visible size increase. This is extremely discouraging, as I feel ALL guys my size have at least 15" arms. I do 3 sets of dumbbell curls (hammer and normal) with 8-10 reps, usually 1-2 times a week. For triceps I do skullcrushers and dips. I also do compound exercises that incorporate these muscles. I feel that something is not right, as with the huge weight gain I should've seen SOME increase. I haven't been eating as much, due to my recent full time employment, but still manage about 3.5k calories a day.