I used to have the same problem. I would pit out all the time even when not doing anything active. I tried shaving my pits and all the various antiperspirants: white ones, clinical strength ones; didn't matter. I would sweat through it and ruin yet another shirt with white mineral sweat stains.
I did what ksuowl did and went to doctor. Got Drysol initially, now it's hypercare. It works.
I don't think some of the posters understand there is sweat, and there is hyper-hydrosis. Excessive sweating makes you self conscious and frustrated. It's not as simple as shaving or switching otc brands of deodorant or antiperspirant, or wearing certain clothing. It's not about odor or hygiene, it's about driving your car and feeling sweat running down your side or lifting your arm and having massive wet stains less than an hour after putting it on--even though you are wearing an undershirt and maximum strength antiperspirant. Again, frustration.
The prescription stuff works on this. No more ruined shirts, no more feeling self-conscious for pit stains. Plus, it doesn't absorb into the bloodstream and stays in the outer layers of the skin--no worries about aluminum toxicity.