Amplifying Signal From Electret Microphone
2 wires or 3?
Polarity known to be correct?
What DC feed voltage?
100k sounds high.
Try 10k
Sensitivity ratings are usually wrt 1V/Pascal = 1 V/ 94 dB Sound Pressure Level.
1V/Pascal = 94 dB SPL = &quot;loud and close&quot;
Real world sensitivities may be 40 - 70 dB below that (!).
-60 dB ~= 1 mV/Pascal.
-40 Db ~= 10 mV/Pascal.
This may not be far off what you are seeing depending on the mic you have and what signal level you require.
So with a 200V/V amplifier and a loud signal you'd expect about 200 mV from a -60 dB sensitivity microphone with a rather loud signal.
And 2V with a -40 dB mic.
Microphone output and gain calculator here

Nicely done amplifer article here - note input DC bias resistor needed for electret.
Many potential circuits here BUT you need to have some idea of basic specs and correct connection.
Example Hosiden mic spec sheet - all at -45 dB sensitivity.
2 transistor electret mic preamp useful.
Another similar useful