MY husband's shirts used to come back from the cleaners with a foul underarm odor, then I read a tip somewhere about spraying underarms of shirts with vinegar water before washing. I mixed clear vinegar with water 50/50 in a spray bottle and saturated the underarms of all his shirts before taking to cleaners or washing at home. When I picked up shirts from cleaners they asked me what I had done, because the shirts no longer smelled bad during pressing. Very cheap, easy and effective, and it never affected color either.
Some deodorants can help remove stained underarms on your clothing. This is a page about use deodorant to remove underarm stains.
Hydrogen peroxide and sunlight may help your remove stubborn yellow perspiration stains. This is a page about cleaning underarm stains on white t-shirts.
This is a page about using aspirin for sweat stains. Sweat stains on clothing can be difficult to remove.