I know exactly what you are talking about because I have lived with this issue (head pressure/pain) since a child but never knew it was NOT normal to get extreme pain and pressure when using the bathroom. So I never mentioned it to my parents because thought it was normal. Long story short, in my 20's I started having other issues, fainting, dizziness, eye pain/pressure/blurry, tight throat/choking and some other issues. Four years later and 20+ specialists I was finally diagnosed with Chiari Malformation which can only be seen on a MRI scan of the brain and neck. I am NOT telling you this to scare you but to share because it can be very frustrating to have doctors dismiss you or not have a clue to what the problem is and many neurologists do not even know what Chiari is but it was discovered and named in the 1800's. Look up Arnold Chiari Malformation and look at the symptoms and see if you have any of them. Everyone with Chiari is different with what symptoms bugs them the most but head issues are #1. Mine being extreme pain/pressure tingling when I exerted too much straining.