Digital Multimeter not working on higher frequency
The AC range on most cheap multimeters is primarily designed to measure 50/60 Hz AC, like you would get out of an electrical outlet. The only specifications I could find for that model of meter specify the AC range as being good for "40 ~ 400 Hz".

If you want to measure the amplitude of a higher frequency signal -- including any signal which includes components at higher frequencies! -- you will need to use a different instrument.

(As an aside, your body is not a voltmeter. Do not use your fingers or tongue to attempt to measure voltages -- it is not an effective means of measurement, and you will injure yourself when you inevitably try to measure an unexpectedly high voltage.)