Hope this helps.
Headaches like most illnesses can be divided into primary and secondary causes.
Primary, which is what I suspect you fear, would mean something actually wrong in the head..this would need an MRI scan to confirm or otherwise. Blood tests would not directly show a tumour in the head. A high ESR could mean temporal arteritis, but believe me if it came back high with relevant symptoms you should be called immediately and started on steroids as blindness may ensue. Migraines starting in an older person, over 40, who has never had them before, should be investigated properly. Let me just say this is the least likely cause.
Secondary. This means the headaches are secondary to something else, and frankly that could be anything, but with an 8 day wait, it is not likely to be serious. Remember that GPs have an obligation to act rapidly and refer within 14 days if something serious is suspected.
Headaches are very common for a GP. Most of the time nothing serious, from dehydration, stress, to referred pain from a bad neck. Worth getting eyes checked if migraines have visual disturbances. High blood pressure can present with headaches but again not that common unless very high. Bottom line is it sounds ok but worth getting checked out properly.