This is a good question. It is important that you make an appointment with your primary care doctor
to have a full history and physical as it is impossible to know what it is without examining it. There are a few possibilities for what could cause a non-traumatic big bump on your head that is only slightly painful when pushed on. The first is a cyst, which is a fluid filled sac under the skin. These are usually benign but can become infected. If this occurs, a general surgeon
may have to perform an incision and drainage to relieve the loculated infected fluid trapped under the skin. The other possibility is a lipoma, which is a benign fatty tumor that can occur anywhere on the skin. Another more rare case of your symptoms are skull based lesions, such as an aneurysmal bone cysts (ABCs). Again, because it is impossible to know what is causing your symptoms without examining you, knowing your gender, age and other related medical conditions. Therefore, it is very important that you make an appointment with your doctor to get a correct diagnosis and obtain appropriate treatment.