Seasonal allergy relief symptoms and conditions

I was given a sample pack of Singulair from my GP for seasonal allergy relief. I take Zyrtec and Flonase on a daily basis anyway. The Singulair was suggested in addition to the regular medications, only temporary. I have been on it for 4 days and feel terrible! Have itchy throat, trouble sleeping through the night, although I am VERY tired, can't focus, swollen eyes and NOW red eyes...my boss just suggested I go home from work again to get some rest. I bet they think I drink during lunch! This is terrible and I will stop taking this tonight. I'd rather deal with seasonal allergies than this...