I am so sorry you are going through this. I know how debilitating and lonely this journey can be. I hope you have found doctors who have helped you by now, but just in case you have not - I wanted to share my experience. I also had severe head pressure (not a typical headache)- along with other symptoms and I was finally referred to Mayo's neurology department and they found that I had a CSF Venous Fistula which was causing a spinal fluid leak. These types of leaks are difficult to detect so most hospitals and doctors are not able to perform the correct tests/procedures to locate this issue. I say that because doctors in my local city thought they could help me, but all the things they did (lumber punctures, blood patches, etc) made all my symptoms much worse. I hope you find the cause of your issues and you can get relief.