Replaced alternator 3 times in 2 year period what could be causing it to go bad??

Well, the most common problem with alternators that I have had in my life has been with alternators that were not lifetime warrantied. If you buy a 1 year warranted alternator, it's likely that the parts inside are inferior to the lifetime warrantied alternators in the aftermarket stores such as Autozone, Advance Auto, Pep Boys, etc.

So, I would recommend that you make sure that you buy a lifetime warrantied part and that should last a very long time, several years in my case per car that I purchased the alternator for.

This also applies to starter motors and other parts for your car.

If you buy a lifetime warrantied alternator and it still goes bad, then there's something in the usage of it, like high miles or lots of accessories being used all of the operational time, that is causing the brushes to wear out prematurely.