I'm not a doctor, of course, so here's what I did in response to your question, Kate. I looked up in Google (though any search engine will do) for "natural remedy for runny nose".

The site I like best from the page one results is this one...
https://www.livestrong.com/article/46336-home-remedy-runny-nose-/
which does happen to mention Zyrtec.

The other line of enquiry I would pursue is to do a search for "zyrtec side effects". And I found this...
https://www.everydayhealth.com/drugs/zyrtec
which includes quite a long list of bad things that can happen to you. Definitely worth reviewing that list.

Thanks for your question, Kate. Hope my response helps.

Gary