I wonder if your brake booster (the big, round vacuum can behind the master cylinder) has failed or has lost its vacuum supply. That would make the brakes much harder to operate. Check the hose that goes from the intake manifold to the booster to make sure it is connected and in good condition. Check to see if the diaphragm in the booster unit is good by disconnecting the vacuum supply hose at the booster with the engine idling. The idle should change drastically when you do this, as you are adding lots of un-metered air to the engine. If there is no change in the idle, that would suggest the diaphragm in the booster is ruptured. Also, check to make sure the vacuum supply hose is not internally blocked by placing your thumb over the end of the hose you disconnected with the engine running. You should feel a strong vacuum. If not, the hose is blocked.