This sounds like you have a bad booster on the brakes. It is not giving you any assistance. I would change it and see what happens. If you still have issues after that you may need to bleed the brakes all around the car starting with the right rear and then work your way around the car. This should insure that you have all the air out. If after doing that there is no improvement then the master cylinder would be the final item in the system that may be bad. I don't think you will need to go that far though.