If you go to the vet and they say there is no parasite, I would def. switch foods. 20 poops a day isn't normal. Also, if you were able to walk him a few times a day that might help. I read an article once that talked about how walking helps both human and dogs digestion, and if "nature calls" you'll have a dog pooping outside. When he sees the praise he gets maybe he'll do more and the situation will be alleviated.
Good luck
