My son has been pooing non stop the last 24hr. He seems fine otherwise. The poo is a yellow and watery and smells sickly. He's 6mths and formula fed?

Diarrhea. It seems like your son has diarrhea. There are many causes for diarrhea and most common at this time of year is simple rotavirus infection. There are many other viral infections at can cause diarrhea as well as other more complicated issues. If this continues make sure that he is properly hydrated with electrolytes (pedialyte) & get him checked out by his pediatrician.
Hydrate. It is important to monitor for dehydration. Is he having wet diapers? Is he able to drink well without vomiting? Formula that is milk based may not be the best choice. Offer pedialite and a lactose free formula such as soy. If there is blood or diarrhea lasts longer than 3 days or if urine out is low then see your doctor.