Is the moisture that comes out of the anus and stains the clothes with the color and smell of feces a natural occurrence that happens to everyone, or is it a condition specific to the questioner?

What the questioner finds on his clothes is normal sweat, not something discharged from the anus. It is necessary to perform a sufficient istinjāʾ (cleansing) after relieving oneself until the area becomes rough. One should not pay attention to this moisture, even if one used three stones for istijmār (cleansing with dry objects) and then the impurity was removed. This sweat does not cause harm, as stated by Imam Ahmad. One should be wary of waswasah (whispers of the devil leading to obsessive doubts).