Why are my arms still small.?

I do the same work out on my arms twice a week, I do 6 sets of 10 reps lifting 31kgs in a standing cable curl and in between I alternate between Dumbbell hammer curls and rotating dumbbell curl lifting 10 kgs per arm i have been do this work out for 3 months and haven't noticed any growth. any help would be good. If there are any decent creatine supplements i should think about etc etc