Brakes not working as they should

I changed my brakes all the way around. I have
front disc and rear drum brakes.
I Bled them starting from the furthest away from
the master cylinder and worked my way to the
front . They worked Good. After a week it seem like
they needed bled again. I checked the fluiid and
added some. My brakes don't work until I press
halfway down on the brake petal, if I go alittle
further and to the floor it seems like they stop
working until I lift up and press again but still only
works when petal is pressed halfway down and
barely slows you down when to the floor. I  noticed
my ABS light was on so I looked around some. I
found that my rear passenger side abs wheel
speed sensor was missing it's bolt and was just
hanging there out of it's correct place. Could this
be causing air to get into my braking system?