This makes no sense

I use the off brand equivalent of Zyrtec daily for my general allergies.  Last year I got a 300-tablet bottle which is almost gone now, so I wanted to look into ordering some more.  When I ordered that bottle, I was able to get it for like $45 through my prescription coverage at the time, which has since changed when Ridge switched health plans last spring.

So today I go to Medco's website, which is our current prescription company, and look for Zyrtec under "Nonprescription items", thinking that because you don't need a prescription for it at a drug store, that's where it'd be.  I couldn't find it, or it's generic equivalent, so I called Medco about it.

The lady I talked to told me that it'd be $87 for a 90-day supply, and I'd need a prescription for it.  I said huh???  You don't need a prescription for it at the drug store, so why would I need one to get it mail order?  She said that's the only way it's covered by insurance.  I told her how last year it was significantly cheaper than that to get it from a prescription company's over the counter section.  I told her it seemed really odd that I'd need a prescription for a non-prescription medicine, and she said that's the only way it's covered.  Um ok.

I just looked on drugstore.com, and on there I can get a 120-day supply for $20.... 4 times lower cost for 33% more, plus I don't need to go to my doctor and get a prescription!  How very strange.  This just sort of baffles me, but I'll just write it off as Medco trying to get more of my money, and shop elsewhere.