Voltage multiplier problem
As prompted a couple of times in the comments, the Typical Forward Voltage chart you've added shows that at room temperature you need 0.8 V to get any significant current through those diodes. You are only feeding the circuit with 100 mV hence the diodes don't conduct and you don't get any multiplication.

Your ideal equation

$$ V_{out} = 5V_{in}-\frac {n-1}{Cf}I_{out} $$

(which I haven't verified) does not account for diode voltage drops, as far as I can see. The equation will only hold true when Vin >> 0.8 V.