Bumps on your head can be caused by anything from injury to a skin condition. There are also some diseases that can cause such bumps, but the only way of establishing what is ailing you is by talking to a doctor for the right diagnosis and treatment.
My cousin had a bump on her head and she waited about a day or two to see if it got better but it didn't so she went to the doctor and he said it was a cyst (which isn't bad) and that he would just numb her and remove it. She was in and out in about 2 hours. Nothing bad just see a doctor if I doesnt get better.