Driver side rear brake caliper screwed?

[1slowdsm]

1993 Talon TSI awd. Stock brake rotors, calipers, lines...stock everything for that part of the car.

I just changed my rear brake pads about a month ago and now the driver's side rear inside pad is out...again. Is my piston in my caliper busted or is there another problem? The outside pad is still almost brand new and the passenger side is the same. I've heard about some sort of rebuild kit, but would be be better to just buy a whole new caliper? I really dont like changing the rear pads once a month, and the money spend eventually will cost the same as buying a whole new caliper to begin with. And I dont think that the inside pad is ever off the rotor. I'm getting TONS of brake dust on that one wheel and plus, its got like a day left before its nothing but metal to metal contact on the rotor. I'm gonna put my car away for a bit until I get some stuff replaced so any help will do....