Why do I have pain in my arms?

Okay,I’d be sitting at the computer typing away at my fanfiction or clicking the mouse.Then I would feel a pain in my arms. It’s directed in one spot. Usually on my right arm it is right under the elbow on the inside of my arm. On my left arm, it’s on the top of my arm and right under my wrist.Not very intense pain but like a doctor’s mallet hitting my knee.But not on my knee,on my arm.
What’s going on?