My left biceps is bigger than my right biceps. I need an advice, please

[Rubenz342]

I'm 17 years old, and I started weightlifting last year. For now, I'm only working on my arms. But somehow, my left biceps got bigger than my right one, the weird thing is that I'm right-handed. Both my arms lift the exact same weight, and I move both arms the exact same way when lifting. Also, when lifting, I start to feel pain in my left arm first, only then I feel pain in my right arm. What am I not doing right? Please, answer.