It's hard to avoid pit stains entirely during the heat of summer, but with the right antiperspirant routine, you can certainly keep yourself from getting too swampy under there. At least, if you're applying it the right way. According to Reviewed, antiperspirant application isn't as brainless as you might have assumed. If you're soaking through all your shirts, you probably just need to rethink your routine.
As opposed to deodorants, which just cut down on odor, antiperspirants are designed to physically block you from sweating. They use compounds like aluminum zirconium tetrachlorohydrex gly to plug up the sweat ducts in your armpits so that you sweat less. Because of that, you have to apply them before you start sweating.
So if you're rolling on antiperspirant right after you shower in the morning, it's not going to do a great job of plugging up those ducts before you start the day. Ideally, you should apply it in the evening, before bed. Your body is at its coolest at night when you aren't moving around much, and that will give the antiperspirant the best chance to get into those sweat ducts.
While you may be afraid that your antiperspirant will wash away when you shower in the morning, don't worry about it. By the time you wake up, the active ingredient will have been pulled into your sweat ducts, and the sweat-blocking properties should last around 24 hours, even if you shower.
Meanwhile, if you use a pure deodorant (without antiperspirant ingredients), you should apply that one after you shower, or the active ingredients in it designed to neutralize bacteria will probably wash off. Or skip the stick altogether and go straight for a microbiome spray.