Hello. thanks for asking from HCM. I can understand your concern. This lump over left side of head could be : swelling in scalp like sebaceous cyst, lymph node, dermoid cyst. These all are non traumatic in origin. : If swelling is hard and feels like attached to bone, it could be bony lesion like osteoma, fibrous dysplasia. From your history, it is not clear whether it is soft/firm/hard, exact location and size. But by relating your lump with above swellings, you can reach unto some conclusion. All these swellings are benign. Do not worry. Surgery is required only if large size, pus in it, looking ugly or you want to get rid of it. Usually, these do not cause such large area pain. Sometimes pain may occur in swelling only. You can leave it as such. Exact diagnosis can be confirmed by tissue sample. Hemicranial headache on left side could be due to migraine/neuralgia. But if your headache is also occurring in neck and radiating to limbs also, it could be cervical spondylosis. You can reach unto some conclusion based on few points : Pain sharp shooting, radiating to neck and left hand, occurring more on neck flexion, coughing, sneezing, not related to light at all, it could be cervical spondylosis. For it you have to avoid neck flexion, weight lifting of any kind, take bed rest, show it to doctor who may advise MRI cervical spine. Some painkiller medication may be prescribed. : Pain on left side, pulsatile, increases in light, fear from light, not related with posture, similar to previous episodes of migraine, it could be Migraine. It can be treated by taking painkiller like Diclofenac sodium after prescription, avoiding bright light, controlling stress. Hope it will help you. thanks. take care.