Help - back mounted rack for a discbrake bike

[man0war]

Need some form of rack on the back of my bike and a fitting bag to carry mostly my gym stuff around [a few tshirts, pants, towels and a book or two]. Dealer said since the bike that I ordered has disc brakes I can't get a usual bike rack for the back wheel, and the Seat-post mounted type isn't stable enough for what I need to carry around or something like that.

Any suggestions ? I'd like to find another solution than carrying a big backpack on my back for longer periods of time daily, especially in this crazy hot weather.

Thanks !

[Tom Stormcrowe]

http://www.amazon.com/Topeak-Explorer-Bicycle-Brake-Mounts/dp/B000FIAVHE