Hi, I am an American Board Certified Neurologist and I am very glad to help you with your health concerns.
Headache is a very common symptom and the good news is majority of the headaches are not due to any underlying serious conditions like brain tumor etc, so despite the fact that it is severe and new onset etc this still most likely not related to any underlying serious conditions like brain tumor.
But considering this is a new symptom so you are supposed to get a CAT scan of the head. I see that they are doing the cat scan of the sinuses and during that time they should include the brain scan too. This way we can find out the precise cause for your headache although the possibility of a brain tumor is very less likely in you for the reasons discussed above. Also brain tumor generally produces other symptoms like seizures, paralysis of the limbs, facial droop, passing out etc and if you are not having these type of symptoms then brain tumor possibility is very less likely.
I am not sure what have you tried to get relief from the pain, since the headache is severe you need strong pain killers like Percocet or Lortab etc which can provide significant relief from this severe pain.
Once again I reassure you serious possibilities like brain tumor appear to be very less likely, however please ask your doctors include cat scan of the head too in addition to the cat scan of the sinuses so that the precise cause for this severe headache can be identified and then treated appropriately and in the meantime you may try one of the stronger pain killers as mentioned above to obtain relief from this severe headache.
Please let me know if you have any further questions; and if you feel you have received the answer to your question please rate me so that I can receive credit for the time and effort put by me in answering your question.