I know what you are going through. my son is almost 6 and when i had to go back to work when he was a baby, things were tough, at the time, my son's dad and I worked opposite shifts, so we didn't have him in a day care, but I missed him SO much when i was at work. I cried a couple of times.
My husband and I seperated when our son was almost 2 and he had to go to daycare, that was tough, I did some research on the place, and it seemed like a good place to go, even spent a few days there before I went back to work then, to make sure that my son liked the kids and he liked them.
And most recently, I was faced with my son's first day of kindergarten. I was so proud of him, its amazing how fast kids really do grow up... He looked so handsome and so confident standing in line, waiting to go to class. As soon as he walked in the door, I cried, my little baby boy has taken the first steps of growing up! The next few days were also tough. Now, he even walks to the school from the parking lot by himself and wants me to wait in the car for him after school, the first time he has done these, I cried too, its so amazing how fast he has matured. I'm just glad he's not embarassed of me hugging and kissing him goodbye yet.
I'm sure your som knows who you are and is very happy to see you. No need to worry, it will get easier in time...