I'm really sorry you had to find that lump. First, call your doctor immediately. There are two things it could be. It could be just fatty tissue (non-cancerous) or it could be the other. Hopefully it's not the other. Get to your doctor ASAP.

You have every right to be scared. Don't think you are overreacting, because you're not. If you need someone to talk to I'm here. My family has a long history of cancer, so I can definitely understand the fear.

Keep us posted.