What are the LEDs you are using? I think you might be misunderstanding how an LED works.
An LED will have a forward voltage drop. You need to choose a resistor that provides the right current (typically 20mA) and drops enough voltage.
So if your supply is 5V, your LED drops 1.2V (typical) and you need 20mA, you get:
R = 3.8 / 0.02
R = 190
So pick something close by from a standard series, e.g. 220Ω.
There aren't really such things as "3v LEDs". You need more data to pick the resistor.