Why are my upper arms so disproportionate?

I've never been overweight in my life, but my upper arms are huge! I am 5'4 and weigh 125 pounds, BMI of 21.5, and I've been as thin as 117 pounds, but my upper arms never shrink. It makes me very upset when I see girls heavier than me with thinner arms. I feel very uncomfortable in tank tops. I've recently begun working out every day and have seen improvement everywhere except my arms. It's getting to point that it's almost making me depressed. I hate looking at myself because no matter how thin I get I still feel fat because of my arms. Is there ANYTHING that I can do to help this? I've tried tricep extensions, weights, push ups, ect. If anyone knows any way please help. I'm trying to get my weight down to 110 pounds to see if being very thin will finally make a difference in my arms.