Suggest Cause And Remedy For Excessive Sweating

I have some condition causing excessive sweating. The cause has yet to be discovered and I've had every test most Dr's have hear of. It's more then an inconvenience and I can sweat enough to cause dehydration. Anyway I've been taking oxybutynin. And for the first month or two it worked great. I went back to working out and could do normal things without becoming dehydrated but it seems not that its working less and less as the time goes on. I've tried taking more then the dose the Dr said but it doesn't seem to help.
Is there anything I can do? I'm beyond suggestions like not eating spicy foods and things that have no effect.