My dog has had an issue with his feces lately (for a month or so). Sometimes it's normal, then about every 3-7 days he'll have either lots of mucus in his stool, or it’s just very light in color and extremely soft, and other times it's watery like. I have continuously checked for visible worms, but find nothing. I don't understand what is happening. His diet has not changed (we only feed him Iams dry dog food). The symptoms just seem to come and go...which is partially why it makes no sense to me. Any thoughts as why this is happening? THANKS!