Brake Pedal Feels Weird

Okay so I have a 1994 Oldsmobile Cutlas Supreme 3.1 engine with just over 136,400 on the dial. For the past week or so my brake pedal goes down further then normal and the car takes longer to come to a complete stop without what it feels like pushing the pedal down a lot. I had all pads done and the rear drivers side caliper and rotor done last August so just about a year ago. I had a mechanic look at the brakes and everything that goes along with it. The master cylcinder checked out and so did the power brake booster. What we did see that my pads where on the low in the rear and that passengers E-brake cable did not open up when released and caused that caliper to seize. At this point I'm thinking to myself okay, that's my problem? Okay fine. I replaced that caliper and both rear pads. I drive out of the shop and the problem continues. I'm at this point close to 400 dollars later I'm totally confused and agrevated i would like some help. The worst is slowing down from coasting and them coming to a Complete stop. On a quick stop the pedal falls just a little bit before it becomes hard and stops the car.