It may be sinusits but ask ur doctor about it. Im a very experienced person in this case as I had sinusits for about 17-18 years yes it can cause very bad headache and pushes everything in head, also pressure on eyes. and it can cause several problems too in the rest of your body like pain in knee or lower back and so on if u swallow pus regularly. it was a very bad experience in my life and i had tried every kind of treatment on the earth which didn't help me. 1-2 month before i had surgery and i feel pretty good. as u are saying your problem is very serious, but i wonder why ur doctor still prefers to treat with antibiotics. as i know antibiotics have many side effects but im not sure if ur symptoms may be caused by them. tell doctor everything next time you visit he/she will help you as its very hard to help from here and we are not proffesionals here, we are just a community of patients. Wish u all the best! hope i helped