Hi. Thanks for your query. Noted the history about your son who is 5 months old. He developed sudden yellowish jelly like diarrhea about a week ago, vomited last night and has fever. All these symptoms are suggestive of an intestinal infection. I would advise you the following in such a situation: Take your son to the Pediatrician for clinical evaluation, examination and tests of blood and stool. If there is an infection, he will be given an appropriate antibiotic, probiotic and whichever is required as per the opinion of the Pediatrician. Maintain a proper hygiene of the nipples if you are breast feeding, of the utensils if he is on other sources of milk.