Hyperhydrosis - sweating with just sitting down

Hello! I sweat in my legs/ass just by sitting down for a bit. All my behind is water-stained and it’s super embarrassing to be outside and go eat because of the water stains on my rear end. Also, all that moisture makes one’s nether regions and in between the legs/crotch area smell bad at the end of the day. I’ve tried scrubbing to remove excess skin, shaving to sweat less, using cornstarch and anti perspirant. I know these are two separate problems but related. What can one do?