Erika,
An MRI or CT scan will not show whether or not you have Migraines. Although some researchers are trying to find biomarkers in the brain that will classify Migraines, these tests currently do not prove a Migraine diagnosis. However, MRI scans are used to rule out any other type of neurological issue that could be causing your Migraines. It doesn't hurt to ask your doctor so that you can have peace of mind.
As far as getting Migraines are certain days of the week, you are not alone. Some refer to them as Weekend Migraines. Getting Migraines on the weekend could be caused by the change in your daily routine. If you sleep longer on the weekend than you do during the work week that can have an impact on your Migraines. Or if you drink alcohol on the weekend or really just do anything outside of your norm. Take a look at your patterns to see if there is anything you can adjust that might help you stay on a more regular schedule (I struggle with this too!).
-Katie
Migraine.com Moderator