Welcome to the forum, phe.
I don't know why you would feel better when you take a decongestant. But if it works, it works.
As NotFound said, you want your azygous (which drains the spine), your jugulars (which drain the brain), and your iliac and lumbar veins (which when blocked shift their blood flow into the azygous) to be looked at.
It's hard to say if you are indeed more likely to have ccsvi in the azygous based on where your spinal lesions are. It seems intuitive, but no proof. Unfortunately the azygous seems to be harder for docs to image. There are new imaging ideas for the azygous, coming from Dr. Sinan out of Kuwait. We've been having a discussion of them over on Dr. Sclafani's thread.
Everyone has a favorite doctor, I have a lot of faith in Dr. Sclafani, particularly for azygous issues.
There is a search button on the top of the page. Doing a search on "Arata" should turn up more on him. He uses IVUS and the larger balloon sizes. (As someone quoted me back to me today, you pick your treatment when you pick your doctor; it is a salon after all. It is wise to put thought into the picking.)