Replying to Altitude sickness help

Kind of a weird situation, but during the 1st and 2nd run of every day of skiing I have had a migrane that has caused me to stop in the middle of the run and sit down for 5 minutes. Its throbbing and lingers for about 30 minues. Happened at Alta, the Bird, and even Deer Valley this week. I drink at least a liter of water before the slopes, 2 liters during, and 2 throughout the rest of the day. I go to Colorado once a year and dont usually get any sort of altitude sickness even when im skiing at 11-12,000 feet. Been taking motrin daily but cant figure it out.

Anyone have any experience with this?