Hi im Joe and 16

I have noticed a painful bump on my left arm near to my elbow, when i press down on the bump it gives pain but I am unable to feel any lump, I also do not remember being bitten, hitting my arm. When i press on it, its painful. Its a small bump and it is the first time i've noticed it.

I'm probably freaking out over nothing and the bump will be gone tomorrow, just wanted any idea on why this random painful bump on my left arm is there.

Thanks