Because you will be starting meds before even going near the mountain, chances are you'll experience the side effects from the meds in time to know that that is really it and not AMS
And other than that, it's true what others have said, different areas, different meds. Go see your doctor.
The best advice I can give you is this: If presented with more than one option of malaria prophylaxis, go with the expensive option! Often the expensive meds have much less side effects, something I experienced first-hand in South Africa this summer. Almost all the people on cheap antimalarials got constipation, headaches, nausea and hallucinations, all of us on the expensive option had no side effects whatsoever.
In this instance, it really pays off to spend that extra buck!