Dr. Dray on YouTube recommends PanOxyl benzoyl peroxide acne wash. Use on the underarms in the shower but let it sit for several minutes before rinsing off. Then, use Vanicream antiperspirant, which is unscented. I've started doing this and have noticed a big difference when doing this regularly.

Other things you could try are: 1.) an antimicrobial spray that you can use as needed for killing the odor, 2.) Monkey Butt powder for absorbing the sweat.