Since allergies are already affecting your sleep, what could it hurt to try? If you feel crappy after a week or two, you know what happened. I would suggest a different antihistamine though. Claritin is now OTC, and does not cause sedation in most. Alleviating your symptoms seems a rational way to handle allergies and improve sleep, it that is an issue.
FYI, it generally takes several doses of a medication to get the best results. The rule of thumb is 5. Claritin is a once a day drug, so you need to take it consistently, since taking it as needed means good relief is a long time coming.