underarms :(

I used to never have to wear deodorant and would never smell. For about the past year and a half I wear deodorant and still have an odor. It's not really like BO it's almost a musky mildewy smell. At least thats the best way I can describe it. Somedays it's worse then others. I can't figure out want the cause may be. I shower everyday, sometimes after I shower they still have a slight smell :(

It's kind of embarassing....any thoughts on what may be causing this and what I can do to stop it??? I use a aluminum free deo and it doesnt work very well.