icharry, for years I would go to altitude (over 8,000 feet) and suffer extreme headaches for three days, until I would get acclimated. A hiking/climbing buddy of mine told me his secret to avoid the severe headaches--aspirin.
To be effective, he instructed me to start taking two tablets every four hours the day before going to altitude.
Since apparently I am aspirin tolerant, the regimen solved my problem. I've never suffered from the headaches since doing this. I discovered, however, that if I did not take the aspirin a day ahead of my trips, aspirin would not alleviate my headaches.
When I get to altitude, after a day of taking aspirin every four hours, I stop taking aspirin.
I've never tried diamox, so I can't speak to that, but aspirin works for me.
You are at a bit of a disadvantage, because you still do not know how your body will react to altitude. Maybe headaches would not be a problem. Unfortunately, the only way to know would be to not take anything, and find out what happens. Of course, which ever way you go, whether you take aspirin or anything else has its risks, as does not taking anything.
I wish you the best on whatever you decide. It sure is nice to hike Whitney without excruciating headaches or other pains.