How can I relieve pain after having a myelogram with a CT scan?

Mild pain is typical. Pain is usually related to the needle that was used. Heat or cold on the site with otc Ibuprofen as recomended usually helps. However, if the problem is a bad positional (more upright) headache that persists even after resting & drinking fluids (esp. Caffeine) one may have to worry about a "spinal headache' from less fluid around the brain from a leaky puncture site.
Diagnostic studies. Myleograms and ct, as well as MRI scans, are diagnostic studies. They give your doctor the information need to make rational treatment recommendations depending on the information gleemed from this studies. Your practioner who ordered the tests should discuss with you in laymans terms exactly what the results mean, what treatment options would be recommended, and refer you as indicated.
Time, and hydrate. If you are referring to discomfort from the actual lumbar puncture, it should resolve in several days. If you are having a headache, take it easy and drink plenty of fluids. If it persists, a blood patch can be performed.
It is usually self. Limiting. But taking some otc medication and resting that day will help. Heat or ice to the injection site may help. If pain is a headache, most go away within a day but drinking lots of fluids especially ones with caffiene and being supine for 24 hours usually helps.