First, stop googling. Google is not a doctor, doesn't know you and hasn't examined you. You also can't interact or explain your over all symptoms to google. MRI scans and extremely thorough. They are thorough enough to capture neurological conditions like MS, which other types of scans can not see. The MRI could not have missed a tumor. A tumor can be seen in a regular CT Scan image so it would be impossible for the superior MRI machine to have missed it. If you had a tumor that was growing so quickly that there wasn't a trace of it a year ago and its causing severe symptoms now, then you would have been dead already. Its just impossible.
Skepticism is just another way to excuse your anxiety and if you keep making concessions for it, your never going to achieve remission.
Migraines are just that, migraines. They aren't brain tumors. I have migraines, two kinds actually and I have to go in for another MRI this week since my migraines changed and my last scan was four years ago. The doctor doesn't expect to see changes. Brain tumors cause way more symptoms than a migraine.
I also have auras and vision loss and my migraines developed suddenly and out of the blue. They can do that. Its not unusual. They also change with time for some people. I developed ocular migraines after I already had migraine with aura. It happens. You also throw up with migraines and have severe nausea. Anxiety can make migraines worse. Basically nothing unusual I happening to you that doesn't happen to everyone with migraines.