Hi M.,
I did not plan on responding to your request but after I have read the replies that you got so far I decided to write something. If I were you - I would feel even more depressed now.
I would start with saying that however it must be very annoying that they keep calling you, you said your son seems happy there! This would be the most important sign for me that he is being taken good care of!!!!! You didn't write what the director said when you told them these are the normal bowel movements? Have you thought of suggesting that they call your doctor and ask themselves? Btw I have similar experience with my son. His poops are just big and messy. Full stop.
Temperature - keep in mind that he might have had 100 when they took the temperature. He might have been runing or very active or something. Try to look at it that they are trying very hard to protect other children from getting sick and that also means that they will call other children's parents to pick them up to protect your child from getting infected. Try to see it as a good thing!
As for the belongings - you did not write whether they are signed with your sons name? If not - try to write his full name with Sharpie on literaly every item, and pack his things yourself when you pick him up.
Last but not least - perhaps you have tried it - try to befriend his care takers. Be prepared to chat to them for a moment when you pick him up - smile to them, ask how was his day , how was their day, what do they think about his development, do they have any suggestions for you what to work with him on at home, THANK THEM for taking care of your child, tell them how important it is for you and how stressed you are about having to leave him. Get more personal. If they are nice people (and you didn't write anything that would suggest otherwise) it will work!
Again - I understand how annoying it must be, but if your son is happy there - it is worth trying to work on it. In a meanwhile you can search for other day care centers and interview them, just to have a back up. Remember there will be always something that you will not like!
Good luck!!!!!