Hi!
My son started with eye blinking three years at row at same time august/september like your son. First two year tics diseapear at end of Oktober/November but this year he develop more tics like neck/head jerking, It looks like he will develop Tourrete syndrom. One Thing more similar to your son is that my son started to swim class late august and tics are worse. Your observation about august/september is very interested.
AUG/september:
Starting at school
Eating more fruits, tomatoes etc
New harwest for bred baking
Pollen?