You have big losses on those resistors
You should think about changing your setup. Add one battery to pack and...
3x1.5V=4.5V for supply
3x1.2V=3.6V drop on LEDs
18 Ohm resistor for 0.9V on it and I=50mA
In serial setup you should have:
I------------LED---LED--LED--R (18 Ohm)--------I
I I
I---------BAT (-) 3xAAA BAT (+)--------------------I
Losses: 45mW, was 3 x 180mW=540mW
or go for USB
(I took power from molex of PC PSU - its even better)