Welcome to YT and congrats on your new baby
If his diarhea persists, he can get dehydrated really quickly. Also, if he's not eating, he can get hypoglycemia. So, PLEASE do not wait until the 21st if this keeps up...if it lasts more than a day, go to the vet. In the mean time, yes, a tad of pumpkin can help and a little nutrical.
Hope he's doing better!