Can i take clariton d and zyrtec (cetirizine) d together?

Not a great idea: There is likely no added benefit of taking these two medications together. The real question is what kind of symptoms are you attempting to treat. There are other medication that can treat nasal symptoms that are better than antihistamines with decongestant including intranasal steroid sprays. See an Allergist if you would like more guidance on what combination of meds can improve your symptoms.

Duplicate meds: Adding a second antihistamine drug of the same class as the first doesn't make sense. That said, the "double dose" of decongestant (the "D") is not a good idea and side effects escalate markedly. If you're having significant symptoms without relief, it is a good time to see your physician to evaluate your condition.