Yeah, you definitely want to have a resistor on every LED.
I know you said that they were 3v LEDs, but are you sure that you are putting 3v into them?
The higher the voltage, the higher the resistor. For example, if you have 9v, you'd probably want to use a 560 Ohm resistor or thereabouts.
If you're not sure, start with larger resistors first. At worst, a resistor that's too large will just make the LED a little more dull (because not as much current will flow).