What is the purpose of your diode??? isolation of some kind???

Some LCDs will not start bellow 4.5 Volt or so. You have 3 choice...
  1. Use a variable voltage regulator set @ 5.7V and this could work with your diodes
  2. use a diode in serie between GND pin of your regulator and GND with a resistor to the input... but yuk i don't like that method... even if it's working
  3. use 2 voltage regulators