Excessive sweating can be due to a number of causes; such as hormonal, thyroid, stress, side effects to mediations, sugar etc. I don't know your full medical history what tests you may have had done to help rule a medical cause out.
However you do stay it's been this way for several years, did this start to occur when you went into pre-menopause? I would follow up with an endocrinologist.
I'm sure you have tried several kinds, so there is no reason to list some, especially since you have also tried the prescription kind.
Worst case scenario is to have the glands removed.
Hyperhidrosis is a medical condition in which a person sweats excessively and unpredictably.
Here is a site you can read more on this as well.
http://www.sts.org/doc/4097
Hope this helps Hun