Re: please get back on subject, to all
Hi Vannasan. Even though you have specifically asked about Mercury square MC, I agree with Waybread that your issues with public speaking are reflected more broadly in the chart. The thread is about this aspect in your chart, rather than in the abstract, so I do feel its relevant to include an explanation of why Mercury square MC may be problematic in your particular chart.
Starting with the aspect itself, however, a tense aspect from the meridian to Mercury can reflect tense communications between, or involving parents. You may benefit from reflecting on how your communication was received, and how you received and interpreted the communications of others, in the early environment, and how this may have affected you. Mercury being in the first house adds to the suggestion that communication issues were an important feature of your early life in some way.
As well as the Mercury Neptune conjunction, Neptune rules the third house, which reiterates the Mercury-Neptune connection. Neptune, of course is extremely strong in this chart as it is rising, and so Waybread's suggestions may be very useful indeed to you.
Also, as a strongly Capricornian person, you are especially attuned to social rules and standards. The Capricorn Venus Sun conjunction is semisquare Saturn, adding to the possibility of a fear of failure with regard to giving of oneself.
Mercury sextile Pluto may bring a heightened sense of threat with regard to communication, even though the aspect is a sextile.
Mars in Scorpio in the 11th, with Pluto near the 11th cusp, both also in Scorpio - these placements could be projected onto groups, perhaps bringing a fear of being overpowered and defeated. How does your Mars in Scorpio function generally? Are you able to express healthy aggression or does it get suppressed and then look for a way into your awareness through other people. Moon in Aquarius exactly square Mars in Scorpio may instinctively shy away from expressing aggressive or assertive energy of any kind due a fear of losing touch with the civilised ethics and ideals that can be like a symbolic breast to Moon in Aquarius.
All of the above chart factors also reflect your passion for public speaking, and for the sharing of ideas and visions - Moon conjunct Jupiter in Aquarius adding yet more weight to this passion. Your chart also suggests great integrity and I'm sure that will increasingly come across as you continue to work through your fears. I would spend some time reflecting on what it is you are actually afraid of, and who it is that is afraid because this 'who' is just one part of you.
A couple of more things to bare in mind - Firstly, Chiron in Gemini in the 6th house closely quincunx Mercury could add to a sense of a wound around the use of the mind. And secondly, Uranus in the 12th can reflect a family background in which the expression of new and exciting ideas was frowned upon.
All this is speculative of course, and I'd be very interested to hear your responses.
By nature we have no defect that could not become a strength,
no strength that could not become a defect
Every chart is a dog's dinner in terms of consistency of theme