As 70chall440 stated, if it is the rears that you are having the issue with it's almost always the proportioning valve tripped or stuck.
When there is a lack of fluid pressure in the rear the valve is designed to trip and direct the braking to the front. it is very easy to cause this issue while bleeding by pressing the brake pedal too far down on the initial bleeding.
I would try gravity bleeding the rears for a while and then stab the pedal a couple of times with all the bleeders closed. if you have enough fluid volume there it should reset. then you can carefully continue bleeding the system. The key is not to push the pedal all the way to the floor while bleeding the system.
I hope this helps you out.