Assalaamu alaykum. One day, after urinating and making ablution, I noticed a discharge, it was about two drops (on my genitals), however I disregarded what I saw as impossible and considered it Satanic whisperings. Later, on another day, I noticed the same thing and found that it was real! So what should I do about the prayer in that ablution and what about the garment that I wore after the discharge? (I did not wash my genitals. However, I am not sure if the discharge touched the garment, although it very likely did do so.) So what shall I do about the prayers that I prayed in that garment? This occured to me now, but it happened a week ago.

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger. 

You mentioned in your question that you were not sure whether there was an actual discharge or not and only had a doubt, and then your doubt became stronger when you saw an actual discharge a day later. If this is the case, then you should know that there is no harm in that, and you seem to suffer from Waswasah (obsessive whisperings). Muslim scholars have unanimously agreed on a basic principle in this regard, which is: ‘Certainty is not overruled by doubt’ (i.e. mere doubts and suppositions are of no legal consequences). They deduced it from the hadeeth reported on the authority of ‘Abdullaah ibn Zayd in which the Prophet, sallallaahu ‘alayhi wa sallam, was asked about having doubts (concerning breaking the ablution) during prayer. He, sallallaahu ‘alayhi wa sallam, said, “He should not leave until he hears a sound or detects an odor.” [Al-Bukhari and Muslim] Imaam An-Nawawi commented on the hadeeth saying, “The doubt here is that the person imagines that he passed wind (and invalidated his ablution).”

An-Nawawi also wrote, “Muslim jurists underlined that doubt in Fiqh issues related to (purity of) water, invalidation of ablution, impurity, prayer, fasting, divorce, freeing a slave, and other issues denotes wavering between the existence and non-existence of something regardless of whether the two possibilities are equal (in weight) or one of them is more probable than the other. This is the meaning of doubt when it is used by Fiqh scholars in their books.” [Al-Majmoo’]

Hence, what you mentioned in the question does not affect the validity of your prayer; you do not need to repeat that prayer. Also, you are not obliged to wash your clothes because it is a mere illusion, and the fact that drops of discharge came out later does not have any weight in this regard. It remains a mere doubt that does not entail negating the basic principle.

Allaah knows best.