Need advice for my Battery powered DC-DC power supply/ Battery discharger

Always want to build a digital power supply, have tried many times, but all failed terribly, and this would be my fourth attempts. want to get some help from expert out there. Please if you can spot some potential problem, let me know.

Here is what my Power supply should be able to do:
-1.3-20V adjustable regulated output (Spent few hours hacking a step Up/Down board just for it to do that; tested, 4 amp output at 20V)

  • Current monitor using a 5W 1 ohm resistor ( 1mv drop = 100ma )
  • Constant current control (Using above current read out to finely adjust the PWM feeding to the P-Channel mosfet (with this affect my voltage output?? ))
    -Battery dicharger/Test at different discharge rate ( Using the same 5W resistor to discharge a battery through a NPN resistor with its base connect to a PWM pin)