Given that you've already had a CT scan that ruled out sinusitis, it's important to consider other potential causes for your headaches. could be tension-type headaches, migraines, or even a form of secondary headaches stemming from other issues. The fact that the intensity increases in the evening might suggest a few different triggers, including stress sleep patterns, hydration, diet, and stress levels can all play significant roles in headache frequency and intensity. Keeping a headache diary could help identify patterns or triggers specific to your situation. I recommend that you follow up with a neurologist who can take a more detailed history, perform a physical exam, and possibly recommend further testing if needed.