What can one use to help stop armpit sweat?

Do all the normal daily hygiene BUT instead of using vinegar and going around smelling like a pickle or Tomato Juice that only will temporarily solve the odor...USE athlete's foot spray just like you would spray on deodorant. You only have to apply this once and reapply anytime you smell that under arm stench.

Wash frequently, and wear deodorants/antiperspirants or powder under your arms. Keep the area dry and "aired out" as much as possible, because the odor is often caused by bacteria or other organisms (such as yeasts and fungi) that grow in the warm moist area under your arms. If it is very offensive, and doesn't entirely seem to go away after washing yourself, some of the odor may be lingering in the hair in your arm pits. You may consider shaving them and washing very vigorously with soap and water and then use a small amount of rubbing alcohol to thoroughly cleanse the area and kill bacteria on the skin. Washing and soaking in a tub can work better than showering. Then, dry with a towel and let it air dry completely, or even blow with a hair dryer on the low setting. Then once totally dry, apply antiperspirant and deodorant. If you want it to, the hair will grow back with less accumulation of unpleasant odors, or you may decide to keep the area shaved or hair trimmed shorter if very thick and long as a longer-term solution.

Be sure the clothing you are wearing is not retaining stains and odors through the washing. Washing and rinsing the clothes in hot water and a mild mixture of chlorine bleach with the detergent may be needed to be sure the odor is not coming from bacteria or oils held in the fabric. Workout clothes can retain odors like this through washings, so some people soak them in a weak water and bleach solution (read the bleach label for mix ratio) when they take them off until they can be washed properly, that way the soil, stains and perspiration can be removed better during the wash and the odors will not dry in the fabric before washing which makes them harder to wash out later.