My advice is to use a body wash or soap with salycitic acid. It's in products for preventing or treating acne - the salycitic acid kills the bacteria that causes body odor. You can also apply a toner with salycitic acid directly to your armpits (Stridex pads work well for this - they even make ones that are larger for use on the body). I do this and have zero B.O. Some people use other antibacterial soaps like Hibiclens or Paroxyl.
Also make sure that you are wearing clean clothes (wearing the same tshirt a couple of days in a row is taking a chance).
ETA: This won't help reduce sweating but it will help with the bacteria that feeds on the sweat.