Mom, this is just the beginning, wait till kindergarten, wait till first day of middle school, then High school, then college.. It is all exactly the same.
Your son is little, but he will be fine. YOU need to be strong. YOU need to set the tone. If you act nervous upset, concerned and react he can not only see it but sense it.
Daycare is a fun place. It is not scary. It is him that is freaked out because it is a change, but guess what? He will get used to it and eventually is going to love it.
He is going to become a little more independent, he will see what the other kids can do and will want to do it too. Have you considered having another child? If you do, there will be huge changes, but your son will be better prepared, because he will know that changes do not have to be scary.
This is not unusual, even kids in kindergarten who have never attend day care can be like your son is acting now. Your son will have a heads up. He is going to be so proud that he is a big boy and can be a big buddy to the kids that are scared.
Hang in there. I am sending you strength.