Re: Is this oversupply??
If talking to an IBCLC will ease your mind, then you should definitely call.
My son has had a couple viral infections that have produced very fouls smelling stools with odd consistencies. If there is no fever then there may not be an infection or if there is one, it may be very minor and clear pretty easily.
Travel can be pretty stressful and disruptive to the digestive system. Have his nursing patterns changed significantly since you've been gone? That could be related as well.
If your baby seems otherwise okay, then it's probably nothing major. Even if it is oversupply, it's not a problem unless it is causing you problems (e.g. plugged ducts) or him problems (e.g. painful gas).