Finding traces of Najasah in one's clothes

Q: Your Eminence, I have a recurrent problem which bothers me: I usually clean my private parts well after relieving myself but I find traces of feces in my underwear. Sometimes I offer more than one Faridah (obligatory Prayer) with these clothes and I do not repeat what I have performed based on the Hadith of Jibril (Gabriel) when he came to the Prophet (peace be upon him) while offering Salah (Prayer) and commanded him to take off his shoes because they contained filth. Scholars hold this Hadith as proof that when a person offers Salah in a garment that has filth without being aware of that, their Salah will be valid. What should I do about this problem and is it true that I do not have to repeat my Salah?This problem has kept me away from good actions, such as leading people in Salah under the pretext that I might be Najis (ritually impure) and there is someone who is worthier than me to lead the Salah because his clothes are Tahir (pure). Also, I sometimes find drops of dark fluid in my underwear from the front; does this fluid come out of my penis or it is just dirt from the pubic hair? It is worth mentioning that it does not have a smell. Is it permissible to visit a doctor to examine my private parts? I do not know what to do about this problem. Please advise, may Allah reward you with the best! As-salamu `alaykum warahmatullah wabarakatuh (Part No. 5; Page No. 152

A: First, a person who wants to offer Salah must purify his clothes from Najasah (impurity) before commencing Salah. When he is sure of his purity and then offers Salah, his Salah will be valid.Second, if a person is sick, there is no problem if he visits a doctor to diagnose his disease, even if the doctor examines his private parts when necessary.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.