I would suggest increasing your weights.
Personally, I hit 6 workouts on my arm days. (3 bicep, 3 triceps)
And for each workout, I do 5 sets, 10-12 reps each.
Like you should feel like your arms BURN when you are trying to finish your last of your 4th or 5th set. PUSH for it and eventually, you will definately tone up your arms.
BUT remember increase your weights slowly, dont jump from curling 5 to 20s, you do not want to tear a muscle.
Do not worry about "getting bigger" because your arms will build muscles, but not look like fat. For me, I workout heavy weights 6 days a week and I am 5'4" and 113-115lbs. (I dont know if that helps hahas) This is actually the same weight as I was when i was 16, (im 20 now) but the thing was that
I was chubbier because i was 2 inches shorter and never worked out i had HUGE love handles hahahahs but yah muscles WILL weigh more than fat.
biggrin yay (:
Yes, a healthy diet is important too. but not like a starvation diet, more like eating more lean proteins and veggies and getting in your calcium. and drinking water. (:
Hope this works out for you! and GOOD LUCK
biggrin And rememebr progress will take time, you have to be patient, it is different for everyone, and love yourself (: <3