+1 on the Diamox.
It's pretty common for there to be a breakpoint altitude where things suddenly start getting a lot harder. Coming from about 600 feet, the first day I'm fine in Empire (8600) but run out of breath pretty easily in Dillon (9100).
Most of my trips out there have been for work; we fly out, go straight up to Dillon the first day and there's no way to properly acclimate. Diamox helps a ton (if you're not allergic to sulfa drugs), but even after ten days Abasin is tough.
Much better is to take a few days working your way up, playing high and sleeping low. A couple of years ago we drove out, camped at ~6,000 feet and every day hiked at 1,000 feet higher than the day before. Didn't have any diamox, but by the end of the week we were running around at ~12,500 and I felt fine.