What should I do about clothes that have become ritually impure (najis) and about my feeling that something has exited my body while I am in a place where I cannot verify it, knowing that I do not suffer from incontinence?

If your feeling about something coming out of you is merely a doubt, then pay no attention to it and you are not required to investigate. Rather, act according to the default, which is that nothing has come out. However, if you are absolutely certain that something has come out, then you are required to perform istinja' and cleanse with water whatever has touched your body and clothing.