Severe pain in my left arm.?

Hi. I'm fifteen. And I'm anemic. I know that anemia can cause pain in your joints but I don't think this is what this pain is because its consistent. For a little over a week, I've been having a severe pain in my left arm. It's the area past my shoulders but above my elbow. When I move my arm backwards it hurts. If I move my arm while it's beside my body, it hurts. If it's away from my body and I move it, it hurts but it's barely noticeable. The worst pain I feel is moving it backwards or close to my body (forward). My boyfriend massaged my arm yesterday and bended it different ways to try to relieve the pain. I'm double jointed in my arms so he could bend my arms a lot of different ways. My dad today, noticed that my arm looked "puffy" like it's swollen. I don't know if that's from my boyfriend massaging it or from there being something wrong with my arm. The pain is unbearable. I wake up all through out the night from the pain. And I have been sleeping on the other side of my body so that there's no pressure on that arm. Help?