Hi Joys-An,
I've had a similar problem this year, especially with a bad sebum odor emanating from my scalp even after I wash my hair. I've had other embarrassing kinds of odor, too. My solution is to practice more vigorous hygiene, and much more often than I used to. Since I've been going through menopause, I've been blaming the hormone shift for my offensive odors. Hormone therapy has helped some. If you are in the stage of life when perimenopause or menopause are factors, you might consult your OB/GYN.
Frankly, I don't see how MS could be causing a change in odors. I suppose if there is brain damage to the center involving the sense of smell, you might be smelling something that isn't really there. Have you had anyone else confirm the odor actually exists?
It is common for medications to have such side effects. Did you do a medications review with your doc? Have you recently added a new med? It's worth checking out. I had a body odor/scalp sebum problem the first time I took prednisone. It went away after I stopped the steroid.
An overactive thyroid and adrenal conditions can cause body odor as well.
I hope you can get to the bottom of it soon.
Kim