Breaks keep getting tight

In the morning when i crank my car up my brakes are fine. After picking up my passengers and about halfway to school my brakes start getting tighter and tighter until they get to the point to where the brake pedal wont go down, and im having to put the gas pedal to the floor just to go the speed limit. I replaced the brake caliper on one side and this didnt help out any. Does anyone have some more suggestions that might work?

btw; its a '95 mazda protege

It's your flex line. probably got a piece of crud in it or has a crack on the inside causing a blockage. replace both the front flex lines. I recommend upgrading to stainless steel flex line but replacing with OEM is fine and should fix the problem. The reason why it's fine in the morning is the lines have time to release pressure. Let us know how it turns out. Also when you do this take this time to do an entire flush of the brake system with new fluid.