Past week I have had pressure in back of my head along with vertigo, I am worried of a brain tumor 2 years ago I had a cat scan and EEG can back fine?

Likely not tumor. It depends on the frequency and severity of symptoms, but you might consider requesting your doctor to order an MRI brain with and without contrast (it provides better detail of the brain than does the ct).
No. You need to do more scans this time to rule out any new issues. Most time it is not serious, but it is hard to predict without ct or mri.