Hi I M Iman And My Son Is 2 Weeks

Hi i m iman and my son is 2 weeks old. Since 3-4 days he has been suffering from loose motions. Now the loose motions are so loose that yellowish disharge is coming seperately and motion seperately. The doctor has given him colic aid, domstal drops, vogut satchet,taxim-o,walamycin. Due to rectal discharge my son is getting rash near the anal area. For rash i m applying rash cream. Can you please let me know whay kind of infection is this and how many days it will take to cure. Is this condition serious?