Why I still have stuffed nose and can not breath well at night t

2nd year pollen allergy suffer, 1st time to  take Claritin (24 hour pill, take at 5pm) 3 days ago , good at daytime,(no stiffed nose in day time, including take a nap ) but once get ready to go to bed(lay down on bed)at late evening time (8-9pm, my  nose is stuffed again and wake up 3 hours after sleep,  any reason? is Claritin supposed to stop allergy symptom? why work great at daytime and not at night time?

Thanks