Question about allergy medicine

Samantha
I've read in a few places that Zyrtec can be safe. But of course you should ask your doctor. My doc was on the fence. A friend of mine who is almost 6 months pregnant said she was told that she could take it whenever she had bad flare ups of allergies. I'm a chronic allergy sufferer and I had been taking one Zyrtec every day. I went without it for over a week and boy did my allergies come back hard. 
Would it be safe to take one once a week just to keep allergies at bay? 
Thoughts? Experiences? 
I'm currently 4 weeks, 6 days along. 
Thanks!