Do you suffer from 'kafunsho' (cedar pollen allergy) ?
About 20% of the Japanese population suffers from kafunsho. The allergy causes the eyes to go itchy as well as constant runny nose. It hits hardest between early March and late April and is apparently limited to Japan, due the high number of Japanese cedars ("sugi") planted in the last decades following thoughtless government planning.
It is said that people susceptible of suffering from the allergy show signs since their childhood, or for foreigners, after about three years of staying in Japan.