Hey mom123!
In a similar boat myself. Not sure what Effexor XR is, never got put on that one myself. The medication my doctor started me on was a small dose of Topamax to take morning and night. I'm also on many others, but hopefully you're not at that point! My headaches sound different than yours, but make sure if you have pain, you don't take "sorry I don't know for an answer". It could be as simple as sinuses or tension, but make sure you get an answer.
I do believe the CT is the same as a CAT. However, I just came from a MRI tonight and it is amazing the differences between a CT and a MRI.
The CT breaks things down into cross sections of the body (kind of like taking an apple and cutting it into several slices, then looking at each slice to see what's in each section.)
The MRI shows you internal "parts" on a 3D or even 4D level. I was able to get a copy of the MRI on disk before I left the imaging center tonight (you should try that, if anything it's just cool to look at). You actually see your BRAIN! It's freaky! There's also ways to see your nerves, arteries, muscles, etc., but I can't figure that out quite yet - guess that's where the degree comes in!
Hope this helps you!