My medical insurance company is screwing me over??

I went to my pharmacy today to pick up a medicine my doctor prescribed me. I gave the chick my insurance card and she told me it'd be about five while they processed it. A few minutes later she summoned me and told me this medicine was not covered by my insurance because it is an "over the counter" medicine. I then had to pay the ridiculous price ascribed to the medicine.
I find this a little confusing. If this is an "over the counter" medicine, why did my doctor have to write me a prescription for it? Why couldn't he have just told me, "This is the medicine, it is available at your local pharmacy"?
I think this is straight BS, and I think I am being ripped off by my insurance provider to whom I pay my outrageous monthly dues.
I am hopping mad and have already bludgeoned a bedroom pillow- feathers are lying all over my apartment as I type this question.
Is this not BS??? Can someone tell me if I have a leg to stand on should I dispute this with my insurance provider?

While I assume you and us all are being ripped, if it was an OTC they normally don't cover it,

But was it a medication they keep behind the counter or an otherwise controlled drug like ephedrine, or some other cold and flu remedies, are you able to tell us what is was?

That may be why he put it on a prescription, that is simply what he "prescribes" it has nothing to do with insurance covering it or not

Only Medicaid covers OTC meds. Maybe it is a new OTC, and the MD is not familiar with the change. If it is Zyrtec, OTC Claritin is a lot cheaper, or there is prescription Allegra.

If it's over the counter, it's over the counter. Sometimes the doc will put it on a prescription pad so you don't forget what you need.