Should i go see a doctor?

There's like a lump on the back of my neck and it's kind of behind and a little under my left ear. I know it's not a bruise because it doesn't hurt and it's not a pimple because it's under my skin. I'm really worried cuz like a week before i fell on the right side of my head and my neck made a really sick sound, but i still felt okay. Then right after, my right arm started hurting whenever i did a small task like carrying stuff and pretty much anything that involved stretching my right arm out a little. It's possible that i could have gotten this the time i fell, but am i overreacting or is this bad?