Im sorry to hear about your head hurting after your workout. Crossfit can be taxing on your body. Its a lot of intense work that pushes your boby to extremes. Without the right nutritional base and dieting an intense workout can cause head pain in some cases. Once you get into a routine this should go away. I wish you the best of luck! If you need come more helpful tips for crossfit training you might really enjoy taking a look at Intensity and CrossFit | North Rim CrossFit. Best of luck!!
During workouts or after that headache can be occur due to dehydration of our brain cells. Take regular intervals between workouts and drink a plenty of water. Water can save you from workout headache. Use high protein foods like egg, meat and oyster mushroom in the morning.
I am in my 3rd week of CrossFit and just this week have had two mild headaches after workouts. I also remember experiencing these in my earlier years when first engaging in very intense exercise. I found a good explanation of these "exercise headaches" on Livestrong.com.
I remember searching info for headache during hard run (cooper test last spring).
I remember finding something on brains's oxycen deficit during anaerobic work.
This the best I could find now. So their solution is related to breathing.
Exertional Headache After Exercise: Cause and Easy Solution
Personally I would think some more carbs could help, since Cross fit seems to me as very anaerobic carb-sport. (Not doing it so I would not know..)