Pretty common for PhotoReaders to become aware of sensations in the head when they've actively used the system for a while. Tingling, fullness, buzzing, slight pressure. Other than feeling odd for a time by are probably connected to the PhotoReading activity.
There haven't been any fMRI's done on PhotoReaders but I have seen some done on Dyslexic. The interesting thing is with these fMRI's is they showed where the brain activity is when someone is reading, and it is more blood flow into those regions when the brain is doing it right. So I'm willing to guess it's the blood flow you're noticing as new neural pathways are being built as your brain is sorting the information you've PhotoRead.
Drink plenty of water to keep the brain hydrated.
Alex