First, welcome to the forum!
Second, you should know that Metacam is a very dangerous drug for cats. Have a read through this site
http://www.metacamkills.com
Third, considering that this problem has not been diagnosed and that an inappropriate drug has been prescribed without a diagnosis, my recommendation would be that you find a competent feline Veterinarian.
This site will provide a feline practitioner by region
http://www.catvets.com/findadoctor/findadoctor.aspx
This site is a list of Veterinarians who have "proven their worth" in treating very sick cats
http://members.verizon.net/~vze2r6qt/vets/#top
Unfortunately, Vets are not "created equal"!