How often can you buy Claritin d?

It depends - on how much you buy, and where you buy it.
Claritin-D contains pseudoephedrine, which is a federally-regulated substance. Federal guidelines that took effect Sept. 30, 2006 restrict retailers to selling no more than 3.6 grams to an individual in a single day, and impose a 9.0 gram 30-day purchase limit.
So, you could buy Claritin-D on two consecutive days, but assuming you bought the limit of 3.6 grams each day and went to the same retailer, you would only be able to buy 1.8 grams the third day and would not be able to buy any more from that retailer until 30 days has passed.
These regulations do not apply to regular Claritin (without the -D), and some states may have more stringent guidelines in place.

Answer (2)

With a doctor's prescription Claritin can be legally purchased from online pharmacies.
You don't have a prescription? You must visit your physician.

How to Save Money on a Prescription?

Ask your doctor to prescribe a generic medication instead of the name brand. Almost all of them are identical in their active ingredients and can really save money on a prescription.
Shop around at as many pharmacies as possible. Don't forget to include online pharmacies in your search, as they often have the best prices, and you can save a lot of money on a prescription.