Well, your ascendant is in Virgo 17 deg 10 min if it is calculated according to Tropical (Western) zodiac for the given time of birth. There is a daylight saving time of one hour on the date of your birth. For the same time if the ascendant is calculated according to indian method the ascendant is Leo at 23 deg 28 min.
Speech is governed by Mercury, the II house from the ascendant and the II house from Mercury. Thus the three elements in your chart are Mercury, Virgo owned by Mercury and Gemini, again owned by Mercury. Therefore Mercury is the sole element for speech in your chart and whenever there is an adverse influence on Mercury, your speech gets effected.
What is the nature of adverse influence that should cause defect in speech?
The VI house from the ascendant shows defect/disease. Saturn is the karaka for it. The VI house from Saturn would also cause a defect. So the elements are Saturn, Capricorn and Taurus.
You will notice that major-period of Venus is going on since 1991 in your chart. It is the owner of Taurus.Venus is in Cancer where in the navamsha chart Mercury is placed, and Saturn and Venus have exchanged constellations in the chart. Saturn is in Poorva Ashadha and Venus in Pushyami.So Venus in its major-period may cause defect/disease and since it is strongly related to Mercury which is a powerful indicator of speech, the defect would manifest itself in speech. The timing would be determined by sub-periods in the major-periods of Venus.