Sounds like you are adjusting the position of the wheel axle in the frame drop outs to move the rotor relative to the caliper. Your weight and the forces generated going over bumps will push the axle fully into the dropouts, that's why you are getting rub after every ride.
The calipers have an adjustment mechanism and that's how you should adjust the caliper to tune out rub on the rotor. The two mounting bolts go through slots on the caliper which allows the position to be adjusted when the bolts are loosened.
I think you have hydraulic brakes on the Fastroad SL-1. They are slightly easier to adjust that mechanical disc brakes. A good trick for setting hydraulic caliper position is to loosen the bolts so that the caliper can just move, squeeze the brake lever and tighten the bolts (it helps to have a friend squeeze the lever for you).
Park Tool Company has great instruction videos. Try this one. It also will point you to instructions on mechanical brakes if that's in fact what you have.