Sweet Revenge, it is actually the mildest vibration one can use for the third eye.
What you said reminds me of myself when I just started out, when listening to the mantra's was enough to give me a shock through my spine and in my chakra's.
You will become more tolerant to energy as you become more powerful and start producing more bioelectricity.
Eventually advancement will become slow even when vibrating a mantra 108 times.
That is when you are ready for more powerful things, which demons will guide you too when you reach that stage.
The more powerful version of THOTH is THOR and the more powerful version of that is THAUM or THAUR.
THURISAZ is also much more powerful than THOTH and works really well for opening blockages as FakeName has said many times.