parallel has three lights and series has two lights

I understand the equations involving voltage, current, and resistance:  V = I * R and I was powering my circuit with 6 volts and no resistors but I’m not sure how much resistance each LED takes and also how much the switch takes.  Also, I am not sure why I can’t get the series to light three LEDs.  It will only light 2.  Other than that, the pace and level of understanding for me is good.