When you feel that itch, get on some latex free plastic gloves and reach into the rectum until you feel something that seems like a worm and pull it out. They are about half an inch long, white, wiggly if alive, and pointed on one end, hence the name I suppose. I'm sure the net has pictures too.
Try not to panic about the M.S. thing. I was told that too, but it turned out to be thyroid & adrenals which the tests for them were inaccurate about initially. Don't count on the doctors to necessarily understand that symptoms can be far more important than lab tests for parasites & thyroid & adrenal.