Cetirizine, while it is an antihistamine, does not cross the blood-brain barrier and therefore does not have any centrally acting effects.
It's possible that it may cause minor sedation, but it isn't going to be all that powerful. Maybe look through your medicine cabinet and try to find something else. Diphenhydramine is a very potent, centrally acting antihistamine and can cause pretty powerful sedation in doses above 25MG's. If you honestly don't have anything else to take in your medicine cabinets, maybe look through where you keep your vitamin supplements?
Look for Melatonin, St. Johns Wort, Valerian Root, Kava, and others. Even Magnesium supplements will help you fall asleep. If you happen to find any of those; take only one pill of Melatonin as you only need very little to feel sleepy, take around 1500MG's of St. Johns Wort, 6000MG's of Kava (1125MG's of Kavalactones) and probably more Valarian Root than your supposed to as well. Though, I've never tried Valerian Root so I can't input from that perspective.
EDIT:
Don't take all of those at once!! I accidentally worded it to sound like you should take all of those together if you have them...don't! It would be okay to combine Melatonin with any ONE of those, but not all three of those together. If you happen to have all of those I recommend Melatonin + Kava, then the next effective would have to Melatonin + St. Johns Wort. I can't really say for Valerian Root, but I imagine Valerian Root + Melatonin would be fine as well.