Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh

 

You do not have to pray fast. Most probably this is a madhy  (urethral discharge). Ali (may Allah be pleased with him) Narrated: I used to get the emotional urethral discharge frequently so I requested Al-Miqdad to ask the Prophet (peace be upon him) about it. Al-Miqdad asked him and he replied, “One has to perform ablution (after it).” (Al-Bukhari)

 

You should only wash the area sullied with mathy and make wudu’. In case this turns to be uncontrollable and frequented to the extent that you think it is a disease, you may make ablution immediately before the time of prayer and cover your private part with some cotton and pray by taking all your time.

 

In this case, you are supposed to just pray the obligatory prayer and additional supererogatory prayers attached to it. When the time for next prayer comes, you repeat the same process again.

 

Almighty Allah knows best.