[Sluttypatton]

If brake fluid is left open to the air for extended periods of time it will absorb moisture, making it compressable. Usually this is far more noticeable as the fluid heats up. The spongyness of the pedal will depend on how water logged the fluid is.
Whether or not this is the cause of your troubles, I can't say for sure, but it sounds like there is something wrong with the fluid because it is compressable.
Try changing the fluid with brand new brake fluid from a unopened container (make sure it is the same DOT rating as the last fluid). This is pretty cheap, so if it doesn't fix the problem you haven't lost much. Make sure to properly bleed the brake lines.