2005 Mercury Sable Brake issues

About two months ago I had basically everything that has to do with my brakes replaced. Master cylinder, calipers, pads, rotars, wheel bearings ect. Once all of this was replaced my brakes worked like a charm. About two days ago I noticed that my pedal felt mushy but my brakes were still working fine. That is until yesterday. My pedal went all but an inch to the floor. I cannot pump them up. My car still stops completely fine, with the exception of how low my pedal goes. I had someone take off all of my tires to try and rebleed them, thinking somehow I had gotten air in the lines. Once we started bleeding them, we noticed that the fluid was filthy, and had some water in it as well. So we completely flushed the fluid and refilled it with new fluid. Both back brakes bled just fine. However, now the front passenger side is only leaking fluid while the brakes are being pumped. Once I hold the brake pedal down, nothing comes out. The pedal also will not go all the way to the floor while pumping and holding it, it stops about 1.5 inches. It also never held pressure or started to tighten up. At all. So After an hour of repeatedly pumping and holding, we decided to close it up and attempt the front drivers. Once again, we were able to bleed it with no problems. Any ideas as to what is going on?