Brief Answer:
Sedentary life with excess sitting over 8 hours a day
Detailed Answer:
Hi,
You seem to have eczema on the skin over the tail bone. It itches first and then causes pain over the area, or sometimes tingles. Excess pressure there because of prolonged sitting causes this. This is seen for individuals who are obese, have torso and with body fat. It is also seen in people who sit in excess over 8 hours a day and work.
Fungus generally grows in that area where there is excess moisture and grows on the fat. Just keep the area dry with cloth and use over the counter antifungal powder to dry it.